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Mastering KCSE Biology with Comprehensive Topical Questions and Answers

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• February 14, 2020

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Biology form 2 topics.

• Classification Of Living Things
• Balance Of Nature
• Transportation Of Materials In Living Things
• Gaseous Exchange And Respiration

Strategies for answering exam and test questions

Click on the accordions below to see more information about how best to tackle the following question types in your exam.

Multi-choice questions

Things to remember about multi-choice questions

• Read through the options and try to eliminate the ones that aren’t right . Multi-choice questions usually have one option that is obviously wrong, and three or four others that are similar.  It is important to look carefully at how they are worded in order to select the correct  answer.
• Don’t struggle over a question . Do all of the easy questions first and come back to harder ones later to maximise efficient use of test/exam time.
• Answer all the questions . Even if you are not sure, your educated guess may well be correct. It is better to have a go at answering a question than potentially miss out on a mark.
• When you check back through your paper and think an answer is wrong - change the answer . Research indicates that you will probably be correct in doing so.

Short answer questions

Short answer questions range from a sentence or two through to a paragraph in length.

• Keep to the point . Short answers are usually two-three sentences.
• Main ideas . Your answers should incorporate the key points, words, ideas and phrases the marker will be looking for.
• Leave one or two lines after each answer . This is so you can add important points later on.
• Try to answer all the questions .  If you don’t know the complete answer, put down what you do know, as this is likely to get you some marks.

Exam essay questions

The advice here is in four parts: Time allocation | Task analysis | Planning | Presentation

Time allocation

• Use the reading time at the start of the exam to choose which essay questions you will answer .
• Check how much time you might have to answer each essay question , and stick to it. You can come back and add more to your answer in your revision time at the end of the exam session.
• If you haven’t finished your answer, jot down the rest in note form . This will show the marker what you know, and you might get some marks for it.

Task analysis

• Read the question carefully .
• Underline or highlight the content words . What is the topic?
• Pick out the instruction words in the question, e.g. identify, describe, compare and contrast, evaluate. What are you being asked to do with the topic?
• Take some time to think and plan your answer . For example: use the reading time to select which essay questions you will answer. Then use the start of the writing time (5-20mins) to make notes of all the points you remember that are relevant to the essay. General guide for timing: for 30 minutes of writing, allow 5-7 minutes for planning .
• Plan out the structure by organising your points into a logical order :e.g. by numbering them according to intended sequence.
• General writing rule for exam essays - one paragraph = one point . Follow standard essay-writing procedure, e.g. start with a topic sentence that contains your key point, and then support this with examples, explanations, and evidence.

Presentation

• Make sure your handwriting is legible . Markers should not have to decipher your handwriting. If your handwriting is illegible, it could compromise your marks.
• Make sure that you can express ideas effectively in terms of sentence structure and word use .  Incoherent sentences and incorrect terminology will likely result in the marker not being able to understand your answer properly.
• Don’t worry too much about punctuation, grammar and spelling . Getting your ideas down is more important than ‘perfect’ writing (and markers usually take this into account given that students are writing under pressure in an exam situation). However, you do need a basic level of competency in these areas: an answer that lacks any punctuation and is full of spelling mistakes will probably be incoherent for the marker.
• Don't waffle . Get straight to the point in terms of your answer so that you don’t waste time and word space on unessential or irrelevant detail. Planning your essay beforehand is key to avoiding waffle.

Problem solving questions

Usually these types of questions target formulae, steps in a process, or rules.

• Make sure you write down relevant formulas, equations, and rules . Important: For numerical problems involving computation, make sure you include the appropriate mathematical units in your final answer (e.g. ml, m/sec).
• Clearly show the steps you have taken in working out the answers.
• If necessary, write notes to explain your answers .
• Do the easier answers first , and return to the difficult ones later.

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Form 2 Biology Notes

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Biology Questions and Answers - Form 2 End Term 1 Exams 2022

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• Taxonomy (1mk)
• Species (1mk)
• Lysosomes(1mk)
• Golgi apparatus (1mk)
• Plant tissues
• Animal tissues (2mks)
• Name three photosynthetic cells in plants (2mks)
• State three structural differences between arteries and veins(3mrk)
• Give two reasons why clotting of blood is important (2mks)
• Name one enzyme and one metal ion that are required in the blood clotting process 2mks)

• Give two ways in which leaves are adapted to absorb light(2mrks)
• Name the gases labelled X and Y(2mrks)
• Name the tissue that transports water into the leaf and sugars out of the leaf (2mrks)
• Explain why it’s an advantage for the plant to store carbohydrates as starch rather than as sugars(2mrks)

• Name the part labelled Y (1mrk)
• State the function of the part labelled X (1mrk)
• State the role of emulsification in the digestion of fats in the alimentary canal (1mrk)
• What is the function of hydrochloric acid in the alimentary canal? (2MRKS)
• What is meant by the term gaseous exchange (1mrks.
• Name and explain the characteristics of gaseous exchange surfaces. (4mrks)
• State three ways in which leaves of plants are adapted to gaseous exchange(3mrks)
• Explain stomatal distribution in plants of different habitats (6 mks)

• Name the parts labelled A, B and D (3mrks)
• State the functions of the parts labelled C and E (2mrks)
• List three differences between the section above and the one that would be obtained from roots of the same plant. (3mrks)
• Distinguish between guttation and transpiration (2mrks)
• Other than transport, state one other function of xylem tissue in plants (1mrk)
• Identify the part of the heart that initiates the heart beat (1mrk)
• Give a reason why the left ventricle muscles are thicker than the right ventricles muscles (2mrks)
• State the forms in which carbon (IV) oxide is transported in the blood
• Sunken stomata (2mrks)
• Thick waxy cuticle (1mrk)
• Material that strengthens xylem tissue (1mrk);
• Tissue that is removed when the bark of a dicotyledonous plant is ringed (1mrk)
• Why is it dangerous to sleep in an enclosed room with a burning jiko(3mrks)?
• Why do plants not take in oxygen during the day although they need it for respiration (2mrks)
• Draw and label the structure of a gill. (5mrks)

MARKING SCHEME

• Taxonomy (1mk) study of classification
• Species (1mk) lowest unit in classification whose members can freely interbreed giving rise to viable offspring.
• Lysosomes(1mk) Contains lytic enzymes which breakdown worn-out tissues and organelles
• Golgi apparatus (1mk) site for synthesis of lysosomes
• Plant tissues - starch
• Animal tissues - glycogen (2mks)
• Name three photosynthetic cells in plants (2mks) Stomata Guard cells Palisade mesophyll cells
• Give two reasons why clotting of blood is important (2mks) prevents excessive blood loss and, dehydration Prevents entry of pathogens
• Name one enzyme and one metal ion that are required in the blood clotting process 2mks) Thromboplastin. Calcium ions
• Give two ways in which leaves are adapted to absorb light(2mrks) Broad and flat to absorb maximum light Have chloroplast with chlorophyll to trap light. Transparent cuticle to allow light to pass through
• Name the gases labelled X and Y(2mrks) X – Carbon (IV) Oxide Y – Oxygen
• Name the tissue that transports water into the leaf and sugars out of the leaf (2mrks) Xylem – Transports water Phloem – Sugars out of the leaf
• Explain why it’s an advantage for the plant to store carbohydrates as starch rather than as sugars(2mrks) Starch is insoluble in water, hence osmotically inactive; This reduces effect on absorption of water.
• Name the part labelled Y (1mrk) Intergrana;
• State the function of the part labelled X (1mrk) Site for photolysis; contains chlorophyll pigment absorbs light;
• State the role of emulsification in the digestion of fats in the alimentary canal (1mrk) Increases surface area of fats for purpose of digestion;
• What is the function of hydrochloric acid in the alimentary canal? (2MRKS) Accept any two correct Destroys any ingested pathogens; Provides acidic media for protein digesting enzymes (pepsin); Converts/ activates pepsinogen inactive form to pepsin;
• What is meant by the term gaseous exchange (1mrks. Process by which the respiratory gases are passed across a respiratory surface.
• Name and explain the characteristics of gaseous exchange surfaces. (4mrks) Moist to dissolve respiratory gases Has thin membrane to reduce distance covered by the respiratory gases for efficient diffusion Highly vascularized to create a steep concentration gradient facilitating diffusion Numerous to increase the surface area for gaseous exchange.
• State three ways in which leaves of plants are adapted to gaseous exchange(3mrks) presence of stomata for faster gaseous exchange Intercellular spaces/air spaces in the leaf for movement/circulation of air film of moisture around the surface of cells for easy diffusion Broad/flattened shape to increase surface area Thin lamina to reduce distance of diffusion Exposed to air for easy diffusion
• Explain stomatal distribution in plants of different habitats (6 mks) land plants have their stomata mainly on the lower side to reduce water loss but if on both sides then upper side has very few water plants, floaters, have stomata on upper side to enhance water loss in dry areas, plants have leaves with sunken stomata to reduce water loss by transpiration Plants in wet areas have stomata equally distributed on both sides.
• Name the parts labelled A, B and D (3mrks) i. Epidermis ii. Pith iii. Vascular cambium.
• State the functions of the parts labelled C and E (2mrks) C- Transports manufactured food/ products of photosynthesis/ translocate food E- Transports water and mineral salts
• Distinguish between guttation and transpiration (2mrks) Transpiration is the loss of water vapour through stomata, while guttation is loss or exudation of liquid water through hydathodes
• Other than transport, state one other function of xylem tissue in plants (1mrk) support
• Identify the part of the heart that initiates the heart beat (1mrk) Sinoatrio node/pace maker
• Give a reason why the left ventricle muscles are thicker than the right ventricles muscles (2mrks) To generate high pressure to pump blood; to all parts of the body/ to furthest distance;
• State the forms in which carbon (IV) oxide is transported in the blood Hydrogen carbonate (HCO 3 ) Carbonic acid;
• Sunken stomata (2mrks) Sunken stomata form pits; in which water vapour accumulates reducing rate of transpiration
• Thick waxy cuticle (1mrk) Water proof to reduce the rate of transpiration;
• Why is it dangerous to sleep in an enclosed room with a burning jiko(3mrks)? Burning charcoal produces carbon (II) Oxide which combines with haemoglobin to form carboxyhaemoglobin that is stable/ does not dissociate; reducing efficiency of haemoglobin in carrying oxygen leading to death; Rej death alone
• Why do plants not take in oxygen during the day although they need it for respiration (2mrks) During the day there is presence of sunlight which provides energy for photolysis.

Labelling 3mrks Drawing 2mrks, curved gill bar.

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WAYS TO STAY HEALTHY - PART 2

6. Reduce Sitting and Screen Time

Exercise can’t immunize you from your sedentary time. Even people who exercise regularly could be at increased risk for diabetes and heart disease and stroke if they spend lots of time sitting behind computers. Practically speaking, you could consider taking breaks from sedentary time, such as walking around the office/room a couple of times in a day.

7. Consume less salt and sugar

Most people get their sodium through salt. Reduce your salt intake to 5g per day, equivalent to about one teaspoon. It’s easier to do this by limiting the amount of salt, soy sauce, fish sauce and other high-sodium condiments when preparing meals; removing salt, seasonings and condiments from your meal table; avoiding salty snacks; and choosing low-sodium products. On the other hand, consuming excessive amounts of sugars increases the risk of tooth decay and unhealthy weight gain. In both adults and children, the intake of free sugars should be reduced to less than 10% of total energy intake. This is equivalent to 50g or about 12 teaspoons for an adult. WHO recommends consuming less than 5% of total energy intake for additional health benefits. You can reduce your sugar intake by limiting the consumption of sugary snacks, candies and sugar-sweetened beverages.

8. If you drink alcohol, do so responsibly

While an occasional alcoholic drink likely won’t affect your health, drinking too much alcohol can take a heavy toll on many of your organs.

Overconsumption of alcohol can damage your liver, brain, and heart, and also increase the risk Trusted Source of several types of cancer, including breast, colorectal, and liver cancer. Heavy drinking can also negatively impact your mental health.

- Drinking too much can interfere with the brain’s communication pathways, and can affect the way the brain looks and works.

- Heavy drinking takes a toll on the liver, and can lead to a variety of problems and liver inflammations

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BIOLOGY FORM TWO NOTES-Gaseous Exchange

Gaseous Exchange

• This is the process by which respiratory gases (oxygen and carbon IV oxide) are passed across the respiratory surface.
• Gases are exchanged depending on their concentration gradient.
• In simple organisms such as amoeba, diffusion is enough to bring about gaseous exchange.
• CO 2 diffuses out into the surrounding water while oxygen diffuses from the water across the plasma membrane into the amoeba.

Importance of Gaseous Exchange

• Promote oxygen intake for respiration.
• Facilitate carbon IV oxide removal from the body as a metabolic waste product.

Gaseous Exchange in Plants

• During the day, green plants take in carbon IV for photosynthesis.
• Oxygen is given out as a byproduct of photosynthesis and is released into the atmosphere.

Examples of respiratory Surfaces in Plants

• Stomata in leaves
• Roots e.g. pneumatophores
• Lenticels in woody stems

Structure and Function of the Stomata

• They are tiny openings on the leaf surfaces. They are made up of two guard cells.
• Guard cells are the only epidermal cells containing chloroplasts. They regulate the opening and closing of the stomata.

Adaptations of Guard Cells

• They are bean shaped/sausage shaped.
• Contain chloroplast hence can photosynthesize.
• Inner walls are thicker while outer wall is thin to facilitate the opening and closing of stomata.

Mechanism of Opening and Closing of Stomata

• There are three theories that try to explain how the stomata open and close.

Photosynthetic theory

• Starch Sugar inter-conversion Theory. (effect of changes in pH of guard cells)
• Potassium Ion Theory.
• During the day, guard cells photosynthesize forming glucose.
• This glucose increases the osmotic pressure in the guard cells.
• Guard cells draw in water from the neighbouring epidermal cells and become turgid.
• The stoma opens.
• During the night, there is no photosynthesis due to absence of light.
• Glucose is converted into starch lowering the osmotic pressure in the guard cells.
• Guard cells lose water and become flaccid closing the stomata.
• This is under the influence of pH in the guard cells.
• During the day CO 2 is used up during photosynthesis raising the pH in the guard cells.
• In this high pH, enzymes convert more starch into glucose.
• Osmotic pressure of the guard cells increases and water enters into them, making them turgid hence opening the stomata.
• During the night, there is no photosynthesis. The level of CO 2 increases lowering the pH.
• Enzymes become inactivated and starch is not converted into glucose.
• Osmotic pressure of guard cells falls making them to lose water by osmosis.
• Guard cells become flaccid and stoma closes.

Mechanism of Gaseous Exchange in Plants

• Oxygen diffuses from the atmosphere where it is more concentrated into the plant.
• CO 2 diffuses out as a metabolic waste product along a concentration gradient into the atmosphere.
• Gaseous Exchange through the Stomata
• Stomata are modified in number of ways depending on the habitat of the plant.

Xerophytes: These are plants adapted to life in dry areas.

• They have less number of stomata that are small in size.
• Stomata may be sunken, hairy and in some they open during the night and close during the day.

Hydrophytes: These are the aquatic plants (water Plants)

• They have many stomata that are large in size and mainly found on the upper leaf surface.
• Hydrophytes have the aerenchyma tissue with large air spaces to store air for gaseous exchange.

Mesophytes : They are plants growing in areas with adequate amounts of water.

• They have a fairly large number of stomata found on both leaf surfaces.
• Gaseous Exchange through the Lenticels
• They are openings found on woody stems and they are made of loosely packed cells.
• They allow gaseous exchange between the inside of the plant and the outside by diffusion.
• Actual gaseous exchange occurs on some moist cells under the lenticels.
• Gaseous Exchange through the Roots
• Plants like the mangroves growing in muddy salty waters have specialized aerial breathing roots called pneumatophores.
• Pneumatophores rise above the salty water to facilitate gaseous exchange.

Gaseous Exchange in Animals

Types and Characteristics of Respiratory Surface

• Different animals have different respiratory surfaces depending on the animal’s size, activity and the environment in which it operates as shown below.
• The respiratory surface is the basic unit of any breathing system upon which actual gaseous exchange occurs by diffusion.
• Respiratory surfaces have the following main characteristics.
• Must have a large surface area.
• Must be moist to allow gases to diffuse in solution form.
• Have a dense network of blood capillaries for efficient gaseous exchange.
• Have a thin membrane to reduce the diffusion distance .

Gaseous Exchange in Insects

 Insects have their gaseous exchange system made of many air tubes forming the tracheal system.

• Tracheal system is made up of spiracles and Tracheoles.
• Spiracles are external openings found on both sides of the abdomen and thorax.
• Spiracles have valves to control their opening and closing. They also have hairs to prevent excessive water loss from the body tissue.
• Spiracles open into tubes called trachea. Trachea is reinforced with spiral bands of chitin to keep them open.
• Trachea subdivides into finer air tubes called Tracheoles. Tracheoles are in direct contact with body tissues and organs and they supply individual cells with oxygen.
• Tracheoles do not have bands of chitin and therefore they allow gaseous exchange across their thin moist walls.

  Mechanism of Gaseous Exchange in the Tracheal System of an Insect

• Air is drawn into and out of the tracheal system by muscular movement of the abdominal wall.
• When spiracle valves are open, air is drawn into the tracheal system. The valves close and air is forced along the system by muscle movement.
• Oxygen diffuses into the tissue fluid and into the cells.
• CO2 diffuses out of the cells and into the tissue fluid then into the tracheal system.

Gaseous Exchange in Fish

• Mouth (buccal) cavity.
• Opercular cavity.
• Gills are made of a long curved bone called the gill bar.
• Gill filaments arise from one side of the gill bar. They are many and suspend freely in water providing a large surface area for gaseous exchange.
• Gill rakers arise from the other side of the gill bar. They are teeth like and they prevent solids present in water from damaging the delicate gill filaments.
• Blood vessels enter the gill bar and branch into the gill filaments as blood capillaries.
• Operculum is found on either side of the body near the head and it also protects the delicate gills.

Mechanism of Gaseous Exchange in the Gills of a Bony Fish

• Floor of the mouth cavity is lowered increasing the volume of the mouth cavity but lowering the pressure.
• Water flows into the mouth cavity and the operculum closes.
• Operculum on either side bulge outwards without opening. This increases volume in the gill cavity but the pressure drops.
• Water containing dissolved oxygen flows from the mouth cavity to the gill chamber over the gills.
• The mouth closes and the floor of the mouth cavity is raised.
• The remaining water in the mouth is forced to flow towards the gill chamber.
• Oxygen diffuses from the water into the blood through the thin walls of the gill filaments. It combines with haemoglobin for transportation to all body parts.
• CO 2 diffuses from the blood into the flowing water.
• To ensure maximum gaseous exchange, the water flowing over the gills and the blood in the gills flows in opposite directions.
• This is called counter current flow system and it ensures that at all the points, concentration of oxygen is always higher in the water than in the blood.
• If the water and blood were flowing in the same direction, gaseous exchange will not be that effective.
• Where the oxygen is 50% in water, there is no concentration gradient because blood also has 50% oxygen concentration.

Mechanism of Gaseous Exchange in Amphibians

• Amphibians live on both land and water and therefore exhibit the following methods of gaseous exchange.
• Gaseous exchange through the lining of the buccal cavity
•  Gaseous exchange through the lungs
• Gaseous exchange through the skin
• Gaseous exchange through the mouth (buccal) cavity
• Air is taken in or expelled from the mouth cavity by raising and lowering of the floor mouth.
• Lining of the mouth cavity is moist to dissolves oxygen.
• There is a rich supply of blood capillaries under the lining of the mouth cavity. Oxygen diffuses into the blood and is carried by haemoglobin to all parts of the body.
• Carbon IV oxide from the tissues is brought by the blood to the mouth cavity where diffuses out.
• Gaseous exchange through the lungs
•  The frog has two lungs which are connected to the buccal cavity.
• T he inner lining of the lungs is moist, thin and is richly supplied with blood capillaries.
• During inspiration, the floor of the mouth cavity is lowered and nostrils are open. Air rushes through the open nostrils into the mouth cavity.
• Nostrils close and the floor of the mouth cavity is raised. This reduces the volume and increase the pressure in the mouth cavity forcing air into the lungs.
• Carbon IV oxide from the tissues diffuse into the lung while the oxygen from the lungs diffuses into the tissues.
• Frogs have a thinner and moist skin than the toads.
• There is large network of blood capillaries below the skin to carry the respiratory gases.
• Oxygen from the air and water diffuse through the skin into the blood stream.
• Carbon IV oxide diffuses out of the blood capillaries through the moist skin into the surrounding water and air.

Mechanism of Gaseous Exchange in Mammals

• The following structures are involved in gaseous exchange in mammals;
• Nose (Nostrils)
• Chest cavity (ribs and intercostals muscles)
• Diaphragm .
• It has two openings called nostrils which let in air into the air passages.
• As air moves in the passages, it is warmed and moistened
• The lining of the nasal cavity has also the sense organs for smell.
• It is located on top of the trachea
• It is called the voice box. It controls the pitch of the voice.
• It is a tube made of rings of cartilage which prevents it from collapsing during breathing.
• Inside it is lined with ciliated epithelium. Cilia beat in waves and move mucus and foreign particles away from the lungs towards the pharynx.
• As the trachea enters the lungs, it divides into two branches called Bronchi (Bronchus).
• They are found in the chest cavity and they are enclosed by a double membrane called the pleural membrane.
• The space between the membranes is called the pleural cavity.
• Pleural cavity is filled with pleural fluid which reduces friction making the lungs to move freely in the chest cavity during breathing.

Diagrams 

• In the lungs each bronchus divides into small tubes called bronchioles.
• Bronchioles branch further to form air sacs called alveoli (alveolus)
• Alveolus is covered by a fine network of blood capillaries.

The mechanism of breathing

• Breathing is achieved by changes in the volume and air pressure of the thoracic cavity.
• Thoracic cavity is enclosed by ribs.
• Ribs are covered by intercostals muscles.
• The diaphragm is a muscular sheet of tissue below the chest cavity. It curves upwards in the form of a dome shape.
•  Breathing mechanism involves two processes.
• Inspiration (Inhalation) i.e. breathing in.
• Expiration (Exhalation) i.e. breathing out.

Inspiration (Inhalation) i.e. breathing

• This occurs when the volume of thoracic cavity increases and the pressure decreases.
• External intercostals muscles contract while the internal intercostals muscles relax.
• Ribs are pulled upwards and outwards.
• Diaphragm flattens increasing the volume of the thoracic cavity while decreasing the pressure inside it.
• Air rushes into the lungs through the nose and trachea inflating the lungs.

Diagrams page 62

Expiration (Exhalation) i.e. breathing out

• Volume of thoracic cavity decreases while pressure increases. This is brought about by the following;
• External intercostals muscles relax while internal ones contract.
• Ribs move downwards and inwards.
• Diaphragm relaxes and regains its original dome shape.
• Volume of the thoracic cavity decrease and pressure increases.
• Air is forced out of the lungs through the air passages to the atmosphere.

Gaseous exchange in the alveolus

• Alveoli and blood capillaries are made of very thin walls.
• The wall of the alveolus is covered b a film of moisture which dissolves oxygen in the inhaled air.
• Oxygen diffuses through the epithelium of the alveolus, the capillary wall and through the cell membrane of the red blood cells.
• In the red blood cells it combines with haemoglobin.
• Carbon (iv) oxide is more concentrated in the blood capillaries than in the alveoli.
• It therefore diffuses from the capillaries into the alveoli.
• Water vapour also passes out of the blood by the same process.

Diagram page 64 KLB

Percentage composition of gases in inhaled and exhaled air

Regulation of Breathing

This is controlled by a part of the brain called Medulla oblongata .

Factors affecting the rate of breathing in humans

Breathing rate increases during vigorous activity.

Younger people have a faster breathing because their bodies have more energy demand.

Things like anxiety, fear and fright increases the breathing rate.

• Temperature

Relatively high temperatures increase the rate of breathing.  However, very high temperatures reduce the breathing rate.

If there is fever (high body temperature), the breathing rate increases. Some respiratory diseases however, make breathing difficult.

Lung Volumes

• Lung capacity

This is the total amount of air the lungs can hold when completely filled. The lungs of an adult have a capacity of about 5,500cm 3

• Tidal volume

This is the amount of air taken in and out of the lungs during normal breathing. Tidal volume is about 500cm 3

• Inspiratory reserve volume

This is an additional volume attained after having a forced inhalation in addition to the tidal volume. It is about 2000cm 3

• Inspiratory capacity

This is the tidal volume +Inspiratory reserve volume.

• Expiratory reserve volume

This is air removed after a forced exhalation. It can be up to 1,300cm3

• Vital capacity

This is the deepest possible exhalation. This air can only be forcibly pushed out of the lungs.

• Residual volume

This is the air that normally remains in the lungs after the deepest exhalation. It is normally about 1,500cm 3

  Diagram

Diseases of the Respiratory System

It is caused by:

• Allergens such as pollen grains, certain foods and drugs
• Infections of the lungs by bacteria and viruses
• Difficulty in breathing
• Wheezing sound when breathing

Treatment and Control

• Avoiding the causative agents
•  Injection of drugs and oral application of pills
• Spraying directly into the bronchial tubes with a muscle relaxant

There are two types; Acute and Chronic

• Production of thick greenish or yellowish sputum
• Difficulty in walking and sleeping
• Seeking early medical assistance
• Whooping cough

It is caused by a bacterium called Bordetella pertussis.

• Prolonged coughing and vomiting
• Conjuctival haemorrhage (bleeding)
• Convulsions and coma
• Severe pneumonia in the bronchioles
• Ulcers and heart complications
• Emaciation due to repeated vomiting
• Use of antibiotics
• Use of a balanced diet on patients
• Children immunization at early age

It is caused by a bacterial called Streptococcus pneumoniae

• Chest pains
• Deposits of fluids in the lungs
• Use of antibiotics such as penicillin and sulphonamides
• Avoid overcrowding.
• Good ventilation in living houses
• Pulmonary Tuberculosis

It is caused by a bacterium called Mycobacterium tuberculosis .

• Weight loss
• Coughing with blood stained sputum.
• Use of antibiotics such as streptomycin
• Pasteurization of milk
• Immunization using BCG (Bacille Calmette Guerin)
• Use of radiography (X-Ray)
• Lung cancer

Cancer is uncontrolled cell growth in the body causing tumours.

Some general causes

• Inhalation of cancer causing substances such as asbestos
•  Exposure to radiations such as X-rays, radioactive substances such as uranium and substances that alter the genetic composition of the cell such as mustard gas

Treatment and control

• Surgery to remove the tumour
• Radiotherapy
• Chemotherapy
• Use of some drugs
• Not smoking

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Biology Short Essay Free Response Questions

10 min read • june 11, 2020

Jessica Nadzam

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Overview of the Short Essay (FRQ) Questions

The AP Biology exam used to consist of eight long-form free response questions, but in 2019 it was redesigned to consist of only six free response questions. Two of those questions are in the “short” form, and these consist of 50% of the free response score, or 25% of your total score. 

Long story short, those four questions may not be as long as the first two, but they still pack a big punch on your score.

The short essay questions will always be the last four on your exam. They’re very different than the first two in length and point-value, but you can use the same techniques as the others. You still need to know the content and utilize the “essential verbage” to write an appropriate response, but this response will be shorter and take less time to complete. 

You have to write in blue or black ink (for all things that are good, please do not use a pencil), so have a few of your favorite pens ready. You’ll have lots of pages to write on (if you use all of them, you may have written too much), and you’ll be given a copy of the Formulas and Equations Sheet for any calculations you need to do. 

Questions are 4 points apiece, and they typically contain content and problems concerning multiple content areas. Since they are shorter they are less likely to cover multiple topics, but it does still happen. You could initially respond about protein structure in the first part and then end up describing the evidence of evolution by the end of the question. There’s a lot of points on the table, and CollegeBoard will make you work for them. 

Response Grading (from an AP Reader)

There are 16 points for the last four questions of the FRQ test, and they make up 25% of your AP Biology score. So, how are those points calculated and scored? CollegeBoard is fantastic at writing rigorous questions, but they’re also very good at training their graders (called AP Readers) how to objectively score the questions. Readers spend a whole day training to grade just two of the questions (they don’t get to look at the other four at all), and then spend a whole week grading only those questions, eight hours a day . 

A well-oiled machine may be an understatement. The bottom of the line is, AP Readers know exactly what they’re looking for when they’re grading. They read a hundred tests a day (minimum), and if you don’t have the answer they’ve been told is the right answer, they tend to move on pretty quickly. 

While this seems intimidating, it’s actually good news for you - but only if you pay very close attention to the next section on verbiage. You see, the bolded verbs in AP free response questions are just hints as to what AP Readers are looking for in an answer. If you know those verbs backwards and forwards, you will know what type of response AP Readers want. And if you know that, you don’t have to worry about writing something that may be right content-wise, but still missing a point on a technicality. 

Essential Verbiage

There are a lot of verbs used in AP exams to pose questions for students to ponder and rip their hair out over. 

To keep all that hair on your head, we’ve made you a table. It’s pretty easy - if you know exactly what to do when you encounter each bolded verb , you know exactly what to do to answer the question the way the Reader wants to see it. You know how many points it’s worth, and therefore can figure out how much time to spend on it. 

Side note - keep in mind that if a question asks you do something more than once - maybe to describe two factors or explain three phenomenon, you should multiple that # Points by however many things it expects you to do. 

Strategies for 5able Responses

Do you want a 5 on this test? Then here’s what you need to know and be able to do:

Read. The. Question. Carefully. Seriously. You don’t know how many students miss points because they were skimming and missed a critical word. It’s a heartbreaker for Readers, who want to give you that point, but can’t. Also, read the directions carefully. Your papers always say something about how responses on the actual question page will not be scored. Do not write on the question page . You can use it for brainstorming or outlining as scratch paper, but if your words aren’t written on lined paper or a graph or table, they won’t be scored. So make sure you put your answers in the right place! 

Complete. Sentences. Unless it’s an identify or construct or calculate question, you need a capital letter and a period, or the Reader will not grade that response. Period. Outlines, bulleted lists, and drawings won’t be graded unless specified in the question’s directions. 

Circle your bolded verbs . Find them. Figure out which are worth the most points, the least points, will take the longest, will be the quickest, etc. Then, figure out which ones to answer first. 

When you start the test, you don’t have to go in order. If your mind goes blank on question one, skip it . It’s not going anywhere, you can come back to it. But don’t waste time on it when there are others you can definitely answer later in the booklet. 

The identify and graph/draw questions are some of the quickest to respond to because they don’t require complete sentences, and the answers are usually very quick to come up with. Answer these questions first to get them out of the way. 

Time yourself. You get 90 minutes, but it goes by fast. Keep a digital watch that does not beep , and refer to it regularly. Plot how long you want to spend on each question so you don’t waste time in one area and lose points on another question you could have easily answered. Since the short questions are worth half your free-response score, you shouldn’t spend any more than 45 minutes on these four questions, or about 10-11 minutes apiece. 

This is not AP English. The graders are not English teachers. They don’t care how pretty your introduction is or how ~thought-provoking~ your thesis statement is. They just want to finish your paper and move on, so don’t ramble on and on. Skip the fluff and go straight to the point. Don’t restate the question or introduce the topic or regurgitate random knowledge - it won’t get you extra points, it’s a waste of time for you, and the Readers get bored sorting through all your thoughts and writing. 

Label your responses . While you still have to write in complete sentences, please label each response with a, b, c, etc. if the essay question has multiple parts. You don’t even have to go in order, but this helps Readers find your answer so they don’t have to sift and guess what you meant.

COMMIT TO YOUR ANSWER . Readers don’t like wishy-washy papers. Erase the words “might” and “possible” and “I think” from your vocabulary. You could be completely wrong, but if you’re writing about a purple hippopotamus, COMMIT to that purple hippopotamus. Don’t say “I think the purple hippopotamus might possibly maybe do photosynthesis if it feels like it.” That’s wishy washy, and Readers don’t accept that as an actual answer, so they won’t give points for it. Be committed , and loudly proclaim “This purple hippopotamus does photosynthesis!” Ta-da! 

If possible, always give an example. We said earlier not to mind dump and regurgitate, but examples are usually a good way to sweep up an extra point or two if you have budgeted your time wisely and can accurately apply it to the scenario. 

So, now that you know what the Readers are looking for in your responses, let’s talk about the types of questions they will ask you. 

Question Types

The short version of the free-response test has four questions, and each of those four questions has a distinct question type. These are based on “science practices” that CollegeBoard expects students to develop to be more ~well-rounded~ and ~critical thinkers~. Luckily, these questions go in a distinct order, too. Those types and order is as follows:

Scientific Investigation 

Conceptual Analysis

Analysis of Model or Visual Representation 

Analysis of Data 

With this, you can get a good idea of what to expect on the 3rd, 4th, 5th, and 6th question. And if you’re used to studying for the science section of the ACT, you probably recognize these question types. It’s all about analyzing graphs and tables, pulling information from passages, and performing analysis on data. 

Oh, while remembering all that AP Biology knowledge your teacher tried to get into your brain for the past 6-9 months. No pressure. 

Let’s break down what each of those question types is asking for, and the best ways to respond to maximize your time and your points. 

Scientific Analysis - this question will describe a lab experiment scenario, and expect you to be able to describe the biological concept or process involved, identify an experimental procedure, predict results, and justify your prediction.

Conceptual Analysis - in this question, CollegeBoard will present a question that describes a real-life scenario. It will relate that scenario to a biological phenomenon and tell you something has disrupted the process. To get all four points, you will have to describe the biological process that is happening, explain that biological concept, predict the causes and effects of the disruption, and justify your prediction. 

Analysis of Model or Visual Representation may seem like two separate question types, but they will ask you to do the same thing. Both will give you a description of some biological scenario with a visual model. You will be asked to analyze that model, and then describe different biological characteristics of the model, explain the relationships between the different characteristics, identify or draw the relationships within that model, and then explain how the scenario relates to a larger idea or concept. 

Analysis of Data - for the final question of the exam (and then you’re freeeeee !), you will receive data on a graph or table. You will then have to describe the data (twice), evaluate a hypothesis or prediction using the data, and then explain how the experimental results relate to some biological concept. 

These descriptions can seem a bit confusing on their own. Therefore, some examples are provided below. 

Sample Question 1 - Scientific Investigation  

A forest ecosystem has a delicate balance of life. Autotrophs, heterotrophs, and decomposers live together and exchange resources to survive. Sometimes their relationships are mutually beneficial, but sometimes they can be harmful for one species and beneficial for another. Buteo jumaicensis , or the red-tailed hawk, consumes smaller organisms such as small reptiles and small mammals. Recently, the ecosystem has been disturbed by deforestation of pine trees. Hawks typically roost on the crowns of tall trees, and as a result their habitat begins to diminish. 

a) Describe the niche of the red-tailed hawk. 

b) Identify the type of relationship shared between the red-tailed hawk and a common forest mouse. 

c) Predict the short-term impact of the decline of the red-tailed hawk due to deforestation, and how it will impact the rest of the ecosystem. 

d) Provide reasoning to justify your prediction. 

Sample Question 2 - Conceptual Analysis  

The lac operon model is a common phenomenon used to demonstrate the regulation of gene expression. In this model, a gene is essentially turned “on” and “off” to produce proteins only when they are necessary. This allows a bacteria called Escherichia coli ( E. coli) to metabolize lactose. 

a) Describe the gene expression process from DNA to protein. 

b) Explain why operons are an evolutionary advantage over allowing genes to undergo transcription and translation constantly. 

c) Although less commonly used for demonstration, the trp operon is another bacterial operon found in E. coli. Predict what would occur if a lac repressor was used on the trp operon. 

d) Provide evidence to support your prediction. 

Sample Question 3 - Analyze Model or Visual Representation  

Signal transduction pathways occur when cells receive signals from outside their membranes, and transduct those messages through the cell to a predetermined location. These signals are used for a variety of reasons including growth, division, mating, protein production, and more. In order for a cell to experience signal transduction, it must receive some signal that binds to a receptor and triggers the pathway. 

a) Referring to the figure, predict a possible response that may occur as a result of this signal. b) Describe the steps of the signal transduction pathway that must occur to elicit a response. 

c) Sometimes secondary messengers may enter the cell only after a ligand has bound to a receptor. Explain why secondary messengers may be necessary for cell signalling. 

d) Identify the ligand in the figure. 

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Biology Notes, Revision Questions and Answers  |  Secondary School

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KCSE 2023 Biology Essay Questions and Answers (KCSE 2023 Prediction Questions)

Here are KCSES 2022/2023 Biology Essay Questions and Answers (KCSE 2022 Prediction Questions). Content: 31 pages with 60 questions and answers.

BIOLOGY (231/2) Revision Questions (Essays): Expected Responses

Q1. Explain the various ways in which a typical cell is adapted to its functions

   Has a cell membrane; with pores; that regulates substances entering and leaving the cell; cytoplasm; contain sugars and salts; for maintaining its osmotic pressure; also has a liquid medium; for all biochemical reactions; nucleus; contain chromosomes having hereditary material; and controls all the activities of the cell; ribosomes; are sites for protein synthesis; golgi bodies/apparatus; for secretion of hormones and enzymes; formation of lysosomes; lysosomes; contain lytic enzymes for breaking down worn-out organelles; secretory vesicles; formed from golgi apparatus for secreting substances; smooth endoplasmic reticulum; synthesizes and transports lipids; rough endoplasmic reticulum; transport proteins; nucleolus; controls the activities of the nucleus; produces ribosomes; mitochondria; form sites for energy production; centrioles; formation of cilia and flagella; forms spindle fibres used in cell division; plant sap vacuoles; store salts and other dissolved substances; controls osmotic pressure and turgidity of cells; food vacuoles involved in digestion of engulfed food; chloroplasts; form sites for photosynthesis in plant cells;  Max. 20 mks

Q2. Explain how the various specialized cells are modified to carry out their functions in plants and animals

   Animal cells: Sperm cell; has acrosome containing lytic enzymes; that digest the egg membranes for penetration during fertilization; has a long tail; containing numerous mitochondria; to generate maximum energy for propulsion/swimming in the vaginal fluid after ejaculation; Red blood cells; are flattened, circular/spherical biconcave in shape; to increase the surface area for packaging of haemoglobin; has haemoglobin; that combines with respiratory gases; for transport to and from body tissues; White blood cells; are amoeboid in shape hence able to change shape; to engulf pathogens through phagocytosis; lymphocytes produce antibodies to fight pathogens; Nerve cell; has extensions/dentrites; to receive and send information for sensation; Ciliated epithelial cells; have cilia for propulsion of mucus that traps dust and micro-organisms in the respiratory tract; Muscle cells; elongated, striated and contractile; to bring about movement; Plant cells: Guard cells; bean-shaped; to regulate the size of the stomata allowing gaseous exchange; and control water loss; has chloroplasts with chlorophyll; for photosynthesis; Root hair cell; elongated; thin-walled; with dense cytoplasm for absorption of water and mineral salts; Epidermal cell; thin; for protection of inner tissues from mechanical and micro-organism attack; Palisade cell; contains numerous chloroplasts with chlorophyll; for photosynthesis; elongated; to increase surface area for trapping maximum amounts of light energy; Meristematic cell; thin-walled; with dense cytoplasm; for primary and secondary growth; Max. 20 mks

Q3. Describe how the mammalian body protects itself against infections

   Pathogenic microbes are found on the skin, respiratory tract, mouth, vagina and the intestinal tract; the skin; has a keratinised and waterproof cornified outer layer; that provides a mechanical barrier to microbes/prevents entry of microbes; sebaceous gland; produces sebum; which has antiseptic properties; the respiratory tract; produce mucus secretions that trap dust; cilia sweep/waft/propel the microbes to the pharynx for swallowing or to be coughed out; reflex actions of coughing/sneezing/vomiting help remove foreign materials from the respiratory tract/digestive tract; lysozymes/enzymes in saliva/nasal secretions/tears; digest walls of bacteria destroying them; gastric secretions such as hydrochloric acid lowers the pH in the stomach killing micro-organisms; clotting of blood; prevents entry of microbes after damage of blood vessels; phagocytosis; by phagocytes engulf and destroy microbes and other foreign bodies; lymphocytes are stimulated to produce antibodies; by proteins present in microbes protecting the body; antibodies destroy/kill micro-organisms through various ways: agglutinins; bind to pathogens making them clump together; killing them; Lysins; bind to pathogens and make them burst or disintegrate; opsonins; bind to pathogens making them easily recognized hence be engulfed/destroyed by other lymphocytes; anti-toxins; bind and neutralize toxins produced by micro-organisms; vagina is acidic; hence making it not conducive for growth and reproduction of micro-organisms; Max: 20 mks

Q4. How are the leaves of higher plants adapted to their functions?

    Broad and flattened lamina; to increase surface area; for absorption of light; thin blade; to reduce distance for diffusion of gases and penetration of light waves; transparent epidermis and cuticle; to allow light to penetrate to tissues; cuticle layer absent on stomata; to allow for gaseous exchange; one-cell thick epidermal layer; to reduce the distance over which sunlight penetrates; palisade cells have numerous chloroplasts containing chlorophyll; to trap maximum amounts of light energy; have stomata on the epidermis; to allow for gaseous exchange; and control of water loss through transpiration; palisade layer have elongated cells located at right angles to the leaf surface; for maximum absorption of light energy; spongy mesophyll; consists of spherical and loosely-packed cells; to create air spaces; which communicate with the atmosphere through stomata; for purposes of gaseous exchange and control of water loss; veins have conducting tissues: xylem; for movement of water and dissolved mineral salts; phloem; for translocation of manufactured food; Max. 20 mks

Q5.  Explain how the various teeth adapt mammals for nutrition

   Incisor; sharp; chisel-shaped; for biting; and cutting food; one root for support in the jaw bone; Canines; long; sharp; pointed; for holding prey; piercing; and tearing flesh from prey; single root; for support in the jaw bone; Premolars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food; two roots; for firm support/anchorage in the jaw bone; molars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food; Max. 20 mks

Q6. Describe what happens to a meal of oily beans and maize from the time of ingestion up to the time of absorption

   In the mouth; starch in maize; is digested by salivary amylase/ptyalin/diastase into maltose; food is chewed and mixed by teeth and the tongue; rolled into boluses by peristalsis; it enters into the stomach via the cardiac sphincter; in the stomach, gastric juice containing pepsinogen that is activated to pepsin; digests proteins in the beans; into shorter peptides; food is churned and allowed into the duodenum; via the pyloric sphincter muscle; in the duodenum; bile juice secreted by the gall bladder; emulsifies the oils in the beans into tiny oil droplets; pancreatic juice; secreted by the pancrease; contains pancreatic amylase; that digests starch to maltose; pancreatic lipase; that digests the oil in the beans to fatty acids and glycerol; trypsin; digests proteins into shorter peptides;  food enters into the ileum; where succus entericus is secreted; it contains maltase enzyme; that digests the maltose into glucose; that is absorbed; peptidase; digests peptides into amino acids; lipase digests the remaining lipids (oil) into fatty acids and glycerol; which is absorbed through the lacteals of the villi; Max. 20 mks

Q7. How are the small intestines in mammals adapted to their functions?

Small intestines consists of the duodenum and the ileum; most digestion of food occurs in the duodenum; bile from the gall bladder of the liver is secreted through the bile ducts; and it is used to emulsify fats/break fat particles into tiny droplets; to increase the surface area for enzyme action; the pancreas secretes pancreatic juice to the duodenum; the juice contains pancreatic amylase; that helps to breakdown the remaining starch into maltose; trypsin; (that is secreted in its inactive form, trypsinogen , and activated by enterokinase enzyme); hydrolyses proteins into shorter peptides; pancreatic lipase; converts lipids into fatty acids and glycerol; sodium hydrogen carbonate is also produced; to neutralize the acidic chyme from the stomach; and provide a suitable alkaline medium for pancreatic and other intestinal enzymes; the ileum is long; and narrow; to increase the surface area for complete digestion of food; and maximum absorption of digested food; highly-coiled; to reduce speed of food flow; for maximum digestion; and absorption; presence of villi; and microvilli; to increase surface area; for maximum absorption; dense network of capillaries; to transport blood; for efficient transport of absorbed food; presence of lacteals in the villi; for absorption of fatty acids and glycerol molecules; presence of enzymes: Lipase; for digestion of lipids into fatty acids and glycerol; maltase; for digestion of maltose to glucose molecules; peptidase; for breakdown of peptides into amino acids; sucrase; for digestion of sucrose into glucose and fructose; lactase; for digestion of lactose into glucose and galactose; goblet cells; produce mucus; to lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme; Max. 20 mks

Q8. Outline and explain the various homeostatic functions of the liver in mammals

   Deamination; process of removal of an amino group from an amino acid molecule; the process gets rid of excess amino acids in the body; as the body is not able to store them; the amino group enters the ornithine cycle; where it is combined with carbon (IV) oxideto form urea; which is excreted in urine through the kidney; Heat production; many metabolic activities take place in the liver; releasing heat energy; that is distributed by the blood to other parts of the body; this helps in thermoregulation; Storage of vitamins and mineral salts; Vitamins A, B, D, E and K; are stored in the liver; worn-out red blood cells, are broken down to yield iron; which is stored in the liver in form of ferritin; this is used later in case of shortage; Formation of red blood cells; occurs in the liver of the foetus; the liver also breaks down old/exhausted red blood cells; leading to formation of more in the bone marrow to replace the worn-out cells; to enhance oxygen and carbon (IV) oxide distribution; Regulation of blood sugar level; liver cells convert excess glucose into glycogen and fats under the influence of insulin hormone; the stored glycogen is however converted back to glucose; when glucose levels are low; by the liver cells; under the influence of glucagon hormone; Regulation of plasma proteins; plasma proteins such as prothrombin and fibrinogen are manufactured in the liver using the amino acids found in the liver; they play a major role in blood clotting; that prevents excessive blood loss and infection at the injured area; other plasma proteins produced by the liver such as serum and albumen; contribute to the maintenance of osmotic pressure in the body; non-essential amino acids are also synthesized by the liver; for use by the body; Storage of blood; the liver is highly vascularised; hence it is capable of holding a large volume of blood when the blood vessels dilate during hot conditions; when the temperatures are low, the blood vessels constrict under the influence of the endocrine and nervous systems; hence less blood is stored in the liver; this contributes to thermoregulation; Detoxification; this is the process where harmful compounds such as drugs and poisons; are converted to less toxic compounds in the liver; toxicity is caused by medication, drugs and microorganisms; the toxic compounds are later excreted in urine; detoxification prevents the accumulation of toxins in body cells; which could lead to death or malfunctioning of the body cells; Max. 20 mks

Q9. Explain why the following conditions are necessary for photosynthesis

• Carbon (IV) Oxide

Required in the dark stage of photosynthesis; it combines with the hydrogen ion from the light stage; to form glucose, proteins and lipids; low concentrations reduces the rate of production of energy and food; while high concentrations leads to an increase in the amount of energy and food formed;

It is used to break down water molecules (through photolysis); into hydrogen ions, oxygen and energy; the energy and hydrogen ions formed are used in the dark stage;

• Chlorophyll

Green pigment that traps light energy from the sun; that is used in photolysis of water molecules;

• Suitable temperature and pH

Temperature affects the enzymes involved in photosynthesis; suitable/optimum temperatures activate enzymes; for maximum production of food; while extremely low temperatures inactivate enzymes; leading to less or no production of food; high temperatures denature enzymes; stopping the process of photosynthesis; photosynthetic enzymes work well in low pH; so the rate is high; while higher pH reduces enzyme activity; lowering the rate of photosynthesis;

Forms a medium for the chemical reactions; it is split to yield hydrogen ions, oxygen and energy for use in the dark stage; solvent for the materials used in photosynthesis; Max. 20 mks

Q10. How is the ileum adapted to its functions?

      Long; and narrow; to increase the surface area for complete digestion of food; and maximum absorption of digested food; highly-coiled; to reduce speed of food flow; for maximum digestion; and absorption; presence of villi; and microvilli; to increase surface area; for maximum absorption; dense network of capillaries; to transport blood; for efficient transport of absorbed food; presence of lacteals; for absorption of fatty acids and glycerol molecules; presence of enzymes: Lipase; for digestion of lipids into fatty acids and glycerol; maltase; for digestion of maltose to glucose molecules; peptidase; for breakdown of peptides into amino acids; sucrase; for digestion of sucrose into glucose and fructose; lactase; for digestion of lactose into glucose and galactose; goblet cells; produce mucus; to lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme; Max. 20 mks

Q11. a) What is homeostasis?

         (Mechanisms of) control and maintenance of a constant internal environment regardless of the external conditions; 2 mks

• b) Name any three factors that must be maintained constant in mammalian bodies

          Temperature; Water; Salt or ion content; Carbon (IV) oxide; Glucose; amino acids; Max. 3 mks

• c) Explain how endotherms respond to heat and cold conditions in their environment

         Heat/hot conditions: Increased sweating; to lose heat through latent heat of vaporization; dilation of arterioles under the skin; to bring more blood to the skin surface to lose heat to the atmosphere; decreased body metabolism; to reduce heat generation; erector pili muscles relax; making hair follicles to relax hence hair lies flat on skin, no air is trapped; to lose heat; slow/reduced muscular activity due to slow metabolism; to reduce heat production; panting to expose tongue and mouth; to release heat; moving to shades to avoid direct heat; aestivation; to escape the extreme heat; flapping of ears to create currents to carry away heat; Cold conditions: stamping of feet; to generate heat; basking in the sun to gain heat directly; less production of sweat; to reduce water loss through latent heat of vaporization; vasoconstriction of arterioles; hence less blood flow to the skin surface to reduce heat loss; increased metabolism through release of more thyroxine hormone; to generate heat; erector pili muscles contract; pulling hair follicles hence hair is raised; to trap a layer of moist air; to prevent heat loss; shivering/rapid contraction of muscles; to yield heat to warm body; Max. 15 mks

Q12. Describe the route taken by water from the soil up to the evaporating surface of a plant

      Water is drawn into the root hair cells by osmosis; due to the presence of dissolved substances in the cell sap of root hairs, the concentration of cell sap is greater than that of the surrounding solution in the soil/concentration gradient; this exerts a higher osmotic pressure, thus drawing the water molecules across the cell wall and cell membrane into the root hair cells; more water drawn into the root hair cells dilutes the cell sap; making it less concentrated than that in the adjacent cortex cell of the root; due to osmotic gradient, water moves from the adjacent cells to the next by osmosis; until it enters the xylem vessels located in the center of the root; the xylem vessels of the root then conduct the water up into the xylem vessels in the stem into the leaves; there is a force in the roots which pushes water up the stem; this force is known as root pressure; and can be considerably high in some plants; energy from the endodermal cells of the root is responsible for driving this force; in the xylem vessels, water would rise up by capillarity; to some extent because the vessels are narrower and there is  a high attractive force between the water molecules and the cell walls; the cohesive; and adhesive forces are important in the maintenance of a continuous and uninterrupted water column in the xylem vessels up the tree to the leaves; water vaporizes from the spongy mesophyll cells; their cell sap becomes concentrated than the adjacent cells. This increases the osmotic pressure of the spongy mesophyll cells; as a result of this, water flows into the cell from other surrounding cell, which in turn takes in water from xylem vessels within the leaf veins; this creates a pull/suction force that pulls a stream of water from xylem vessels in the stem and roots. This force, known as transpiration pull; helps in maintaining a continuous column of water from the roots to the leaves; water flows from the midrib into leaf veins from where it enters leaf cells; from the mesophyll cells, it enters the airspaces; then the substomatal air chambers; from where it evaporates through the stomata; to the atmosphere; Max. 20 mks

Q13. How is the mammalian heart adapted to its functions?

Heart is enclosed in a pericardial membrane/pericardium; that produces a fluid; to lubricate it; the membrane also keeps the heart in position; It is covered in a fatty layer; that acts as a shock absorber; made up of cardiac muscles; which are interconnected/interacted hence contract and relax without fatigue or nervous stimulation/myogenic; for continuous pumping of blood throughout the lifespan of the animal; the muscles are supplied by nutrients and oxygen; by the coronary arteries; and the coronary veins take away wastes and carbon (IV) oxide; heart is divided into 4 chambers; for efficient double circulation/ avoid mixing of oxygenated and deoxygenated blood/carry large volume of blood; has interventricular septum; to separate oxygenated and deoxygenated blood; ventricles are thick/muscular; to generate high pressure to pump blood out of the heart; left ventricle has thick muscles/more muscular; to pump blood to all body tissues; heart has bicuspid; and tricuspid valves; to prevent back flow of blood to left auricle; and right auricle respectively; valves have tendinous cords/valve tendons; to prevent them from turning inside out; semi lunar valves located at the beginning of major arteries; prevent backflow of blood into the ventricles; has sino-artrio node located in the muscles of the right auricle; to initiate heart beat/contractions of heart muscles/cardiac muscles, rate of heart beat is controlled by nerves; vagus nerve; slows down heartbeat; while sympathetic nerve; speeds up the heartbeat; has aorta; to transport oxygenated blood to all body parts; has pulmonary artery; that transports deoxygenated blood from right ventricles to lungs for oxygenation; has pulmonary vein; that transports oxygenated blood from lungs to the left ventricles; for distribution to all body parts; has the venacava; that  receives deoxygenated blood from all body parts to right ventricles; Max. 20 mks

Q14. Describe double circulation in mammals

 Deoxygenated blood from body tissues (except lungs); enters the heart via the right auricle; through the venacava; it flows to the right ventricle; via the tricuspid valve; the right ventricle contracts; pumping blood; via the semi lunar valves; through the pulmonary artery; to the lungs for oxygenation; the oxygenated blood from the lungs; flow through the pulmonary vein; to the left auricle; via the bicuspid valve; to the left ventricle; the left ventricle contracts; pumping blood via the semi lunar valves; through the aorta; to the rest of the body tissues; Max. 20 mks

Q15. Describe the process of urine formation in the mammalian kidneys

      The afferent arteriole which is a branch of the renal artery supplies blood to the glomerulus; the afferent arteriole has a wider lumen/diameter than the efferent arteriole; which takes away blood from the glomerulus; the differences in the diameter of the afferent and the afferent vessels causes high pressure; leading to ultrafiltration of blood; the walls of the blood capillaries are one-cell thick; hence glucose, amino acids, vitamins, hormones, salts, creatine, urea and water filter into the Bowman’s capsule; to form glomerular filtrate; white blood cells, red blood cells, plasma proteins such as globulin and platelets are too large to pass through the capillary wall; hence remain in the blood capillaries; useful substances in the human body are selectively reabsorbed; back into the blood stream at the proximal convoluted tubule; the tubule is highly coiled; to increase the surface area for reabsorption of the substances; the useful substances include amino acids, glucose, vitamins, hormones, sodium chloride and water; many mitochondria found at the proximal convoluted tubule; provide energy for reabsorption of these substances against a concentration gradient; the glomerular filtrate flows into the descending and the ascending limb of the loop of Henle; blood in the capillaries and the glomerular filtrate in the loop of Henle move in opposite directions/counter-current flow; this provides a steep concentration gradient that leads to maximum absorption of water through osmosis; sodium chloride is actively absorbed from the ascending limb into the blood capillaries; under the influence of aldosterone hormone; the glomerular filtrate flows into the collecting tubule from where, more water is reabsorbed into the blood stream; antidiuretic hormone influences the amount of water to be reabsorbed depending on the osmotic pressure of the blood; the glomerular filtrate from several collecting tubules now referred to as urine; is emptied into the collecting duct; the urine passes through pyramid, pelvis and ureter into the bladder; where it is stored for some time. The sphincter on the urethra relaxes to allow urine to be released from the body; Max. 20 mks

Q16. Explain the role of the following hormones during homeostasis

• Antidiuretic Hormone (ADH)

Secreted by the (posterior lobe/end) pituitary gland; in response to an increase in the osmotic pressure of blood; the hormone stimulates the distal convoluted tubules and the collecting ducts; to increase their permeability to water; this increases the reabsorption of water into the bloodstream; concentrated and less urine is excreted; when the osmotic pressure decreases, less or no hormone is produced; hence the tubules become impermeable to water; less water is reabsorbed into the bloodstream; hence more dilute urine is excreted; fluctuations in the osmotic pressure is detected by the hypothalamus;

Secreted by the pancrease; in response to a rise in blood sugar level; it stimulates liver cells to convert the excess glucose into glycogen and fats for storage in the liver and muscle cells; increases the oxidation of glucose in respiration to yield water energy and carbon (IV) oxide/increases metabolism in the body; this leads to a fall in blood glucose to normal level;

Secreted by the pancrease; in response to a decline in blood glucose level; it stimulates liver cells to convert the stored glycogen and fats back to glucose; stimulates the conversion of amino acids to glucose; and stops the oxidation of glucose in the body cells; the glucose formed is released to the bloodsteream causing a rise of blood glucose level to normal; Max. 20 mks

Q17. a) Distinguish between Diabetes mellitus and Diabetes insipidus

            Diabetes mellitus is a condition/disease caused by failure of the pancrease to produce adequate insulin hormone; leading to excess glucose levels in the body some of which is released in urine while diabetes insipidus is a condition caused by failure/inability of the kidney tubules to control the amount of water in urine as a result of a defect in production of antidiuretic hormone (ADH) leading to production of more dilute urine; Max. 2 mks

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