Exam-useful questions from this chapter, grouped by marks, each with a full model answer. Try writing the answer yourself first, then check it against this one.
1 1-Mark Questions
Q. Define life processes.
Answer: The processes which together perform the body’s maintenance job, keeping it going even when the organism appears to be doing nothing, are called life processes.
Q. What is peristalsis?
Answer: Peristalsis is the rhythmic, wave-like muscular contraction of the alimentary canal’s lining, which pushes food steadily forward along the gut.
Q. Name the pigment that carries oxygen in human blood, and where it is found.
Answer: Haemoglobin carries oxygen in human blood; it is present in the red blood corpuscles.
Q. What is translocation?
Answer: Translocation is the transport of the soluble products of photosynthesis (and other substances) through the phloem, from the leaves to other parts of the plant.
Q. Define excretion.
Answer: Excretion is the biological process of removing harmful metabolic waste products from the body.
Q. What is the function of guard cells in a leaf?
Answer: Guard cells control the opening and closing of the stomatal pore: they swell with water to open the pore, and shrink to close it.
Q. Name the two different end products of anaerobic respiration, and where each is formed.
Answer: In yeast, anaerobic respiration (fermentation) produces ethanol and carbon dioxide. In our muscle cells, when oxygen is short, it produces lactic acid instead.
Q. What is the normal systolic blood pressure in a healthy human?
Answer: The normal systolic blood pressure is about 120 mm Hg.
Q. Name the basic filtration unit of the kidney.
Answer: The nephron is the basic filtration unit of the kidney.
Q. What is lymph, in one line?
Answer: Lymph, also called tissue fluid, is a fluid similar to blood plasma but colourless and lower in protein, formed when plasma, proteins and blood cells escape through capillary-wall pores into the spaces between tissue cells.
Q. Why do the lungs always keep a residual volume of air, even after breathing out?
Answer: The residual volume gives enough time for the oxygen in the alveoli to be absorbed into the blood and for carbon dioxide to be released from it, with every single breath.
Q. Name any three organs or tissues that can be donated, according to the chapter.
Answer: Any three of: corneas, kidneys, heart, liver, pancreas, lungs, intestines, bone marrow.
2 2-Mark Questions
Q. What is the role of guard cells in regulating gas exchange in a leaf?
Answer: Guard cells swell with water to open the stomatal pore, allowing gas exchange for photosynthesis, and shrink to close the pore when the plant needs to reduce water loss. This lets the plant control how much CO2 enters and how much water vapour it loses at any time.
Q. Why do desert plants take up carbon dioxide at night instead of during the day?
Answer: Taking up CO2 at night lets desert plants keep their stomata closed during the hot day, when opening them would cause too much water loss. The CO2 taken up at night is used to make an intermediate substance, which is then acted upon by the energy chlorophyll absorbs from sunlight the next day.
Q. What is the function of bile juice in digestion?
Answer: Bile juice, secreted by the liver, makes the acidic food arriving from the stomach alkaline so that pancreatic enzymes can act on it, and it emulsifies fats: breaking large fat globules into smaller ones with bile salts, which increases the efficiency of enzyme action on fat.
Q. Why does the small intestine need to be longer in herbivores than in carnivores?
Answer: Herbivores eat grass, which contains cellulose that takes much longer to digest, so they need a longer small intestine to allow enough time for this digestion. Carnivores like tigers eat meat, which is easier to digest, so their small intestine is comparatively shorter.
Q. What is the difference between blood plasma and lymph?
Answer: Plasma is the fluid part of blood, carrying food, CO2 and nitrogenous waste in dissolved form. Lymph forms when some plasma, proteins and blood cells escape through capillary-wall pores into the spaces between tissue cells: it is similar to plasma but colourless and contains less protein.
Q. Why do the ventricles of the heart have thicker muscular walls than the atria?
Answer: Ventricles have to pump blood out to distant organs (the lungs or the whole body) against considerable resistance, while atria only need to collect blood and pass it a short distance to the ventricles below them. This greater pumping job is why ventricle walls are thicker and more muscular.
Q. What is root pressure, and why is it not enough by itself to explain water reaching the top of a tall tree?
Answer: Root pressure is the upward push on the water column in the xylem, created when roots actively absorb ions from the soil and water follows to balance the concentration difference. This pressure alone is too weak to push water to the height of a tall tree, so plants also rely on transpiration pull, the suction created by water evaporating from leaf cells.
Q. What criteria do biologists use to decide whether something is alive?
Answer: Visible movement alone is not reliable, since a sleeping animal or a non-growing plant is still alive. Biologists instead look for molecular movement: the constant, invisible repair and maintenance of an organism’s ordered structures, which is needed because this order otherwise keeps breaking down under the effects of the environment.
Q. What is the function of platelets in the blood?
Answer: Platelets are blood cells that circulate around the body and plug leaks in blood vessels by helping the blood clot at points of injury, preventing both blood loss and the drop in pumping pressure a leak would otherwise cause.
Q. In what important way does dialysis differ from the working of a real kidney?
Answer: A real kidney selectively re-absorbs useful substances, such as glucose, amino acids, salts and most of the water, back into the blood as the filtrate flows along the nephron’s tubule. Dialysis involves no such re-absorption: all the waste simply diffuses out of the blood into the dialysing fluid.
3 4-Mark Questions
Q. Describe the aerobic and anaerobic pathways of respiration, starting from glucose.
Answer: In every organism, the first step is the same: glucose (a 6-carbon molecule) breaks down to pyruvate (a 3-carbon molecule) in the cytoplasm.
If oxygen is available, the pyruvate moves into the mitochondria, where aerobic respiration breaks it down further into three molecules of carbon dioxide and water, releasing a large amount of energy.
If oxygen is not available, anaerobic respiration takes over in the cytoplasm itself: in yeast, pyruvate is converted into ethanol and carbon dioxide (fermentation); in our own muscle cells, when oxygen is in short supply, pyruvate is instead converted into lactic acid, whose build-up during sudden hard activity causes cramps.
In both pathways, the energy released is used to synthesise ATP, which then powers the cell’s other activities.
Q. Explain the structure and function of a nephron.
Answer: Each kidney contains a very large number of nephrons, its basic filtration units. Each nephron begins with a cluster of very thin-walled blood capillaries called the glomerulus, cupped by the coiled tube’s end, Bowman’s capsule, which collects the filtrate that is squeezed out of the blood.
As this filtrate flows along the rest of the tubule, useful substances (glucose, amino acids, salts and most of the water) are selectively re-absorbed back into the blood; how much water is re-absorbed depends on the body’s excess water and how much dissolved waste still needs removing.
The urine that remains passes out of the kidney through the ureter to the urinary bladder, where it is stored until it is released through the urethra.
Q. Describe how food is digested in the human stomach and small intestine.
Answer: In the stomach, gastric glands in the stomach wall release hydrochloric acid, the enzyme pepsin, and mucus. Hydrochloric acid creates the acidic medium pepsin needs to digest proteins, and also kills germs entering with food; mucus protects the stomach’s own lining from the acid.
A sphincter muscle releases the food into the small intestine in small amounts. Here, bile juice from the liver first makes the acidic food alkaline and emulsifies fats; pancreatic juice then supplies trypsin (digests proteins) and lipase (digests emulsified fats); finally, the small intestine’s own wall secretes intestinal juice, whose enzymes complete the job, turning proteins into amino acids, complex carbohydrates into glucose, and fats into fatty acids and glycerol.
Digested food is then absorbed through the villi lining the small intestine, and carried by their rich blood supply to every cell in the body.
Q. Explain how gas exchange in plants changes between day and night, and how it differs between aquatic and terrestrial animals.
Answer: In plants, at night there is no photosynthesis happening, so the main gas-exchange event through the stomata is the release of the CO2 made by respiration. During the day, this same CO2 is immediately used up in photosynthesis, so there is no net CO2 release, and releasing O2 (a by-product of photosynthesis) becomes the main event instead.
Aquatic animals use oxygen dissolved in water, which is present in a much lower concentration than in air, so their gills must work, and they must breathe, much faster than a terrestrial animal needs to, to obtain enough oxygen. Terrestrial animals like humans instead breathe atmospheric air directly, using an internal, moist, delicate gas-exchange surface (the alveoli) protected inside the body, connected to the outside by air passages.
Q. Explain the mechanism of translocation of food through the phloem.
Answer: Unlike the transport of water in xylem, which is largely explained by physical forces, translocation of food through the phloem uses energy. Material such as sucrose is loaded into the phloem’s sieve tubes using energy from ATP; this raises the osmotic pressure of that part of the tissue, drawing water in from neighbouring cells.
The resulting pressure then pushes the material along the sieve tubes, with the help of adjacent companion cells, toward tissues that have lower pressure. Because this loading and unloading can happen anywhere the plant needs it, phloem can move food both upward and downward, according to the plant’s changing needs. For example, in spring, sugar stored in root or stem tissue is transported up to the buds that need energy to grow.
4 6-Mark Questions
Q. Describe, step by step, the flow of blood through all four chambers of the human heart, and explain why this arrangement is called double circulation.
Answer: Oxygen-rich blood from the lungs enters the thin-walled left atrium, which relaxes as it fills and then contracts, passing the blood into the left ventricle. The muscular left ventricle then contracts, pumping this oxygen-rich blood out to the entire body.
At the same time, deoxygenated blood returning from the body enters the right atrium, which contracts to pass the blood into the right ventricle; the right ventricle then contracts and pumps this blood to the lungs, where it picks up fresh oxygen and releases carbon dioxide.
Valves at each chamber’s exit stop blood from flowing backwards when that chamber contracts, and the ventricles have thicker, more muscular walls than the atria, because they must pump blood much further, into the lungs or around the whole body.
Because blood passes through the heart twice for every one complete circuit of the body, once on its way to the lungs and once on its way to the body, this arrangement is called double circulation. It is necessary because it keeps the oxygen-rich and carbon dioxide-rich blood completely separate, giving a much more efficient supply of oxygen than the single circulation seen in fish; this efficiency is especially important for birds and mammals, which constantly use energy to maintain their own body temperature.
Q. Describe nutrition in human beings, explaining the role of every organ and secretion from the mouth to the small intestine.
Answer: Digestion begins in the mouth, where teeth crush food into smaller pieces and the muscular tongue mixes it with saliva; saliva’s enzyme, salivary amylase, starts breaking down starch into simple sugar. Rhythmic peristaltic contractions of the canal’s muscular lining then push the food down the oesophagus to the stomach.
In the stomach, gastric glands release hydrochloric acid (which creates the acidic conditions the enzyme pepsin needs to digest proteins, and also kills incoming germs), pepsin itself, and mucus (which protects the stomach’s own lining from the acid). A sphincter muscle then releases the partly-digested food into the small intestine in small amounts.
The small intestine is where digestion is completed, using secretions from two glands: the liver’s bile juice first makes the acidic food alkaline and emulsifies fats into smaller globules, and the pancreas’s pancreatic juice supplies trypsin (which digests proteins) and lipase (which digests these emulsified fats). Finally, the small intestine’s own wall secretes intestinal juice, whose enzymes complete the breakdown: proteins into amino acids, complex carbohydrates into glucose, and fats into fatty acids and glycerol.
The digested food is absorbed through the many finger-like villi lining the small intestine, which greatly increase the surface area for absorption; their rich blood supply then carries the absorbed food to every cell in the body, to be used for energy, growth and repair. Any unabsorbed material passes into the large intestine, where more water is absorbed from it, and the remaining waste finally leaves the body through the anus.
5 Case Studies
(A) 1 mark What happened to the student’s breathing rate after exercise?
Answer: Her breathing rate doubled, rising from 16 breaths per minute at rest to 32 breaths per minute after running.
(B) 1 mark Why does the body need to breathe faster during exercise?
Answer: Exercising muscles need more oxygen for the extra aerobic respiration that powers the increased activity, and the body must also remove the larger amount of carbon dioxide this produces.
(C) 2 marks If her muscle cells run short of oxygen during intense exercise, which pathway takes over, and what does it produce?
Answer: Anaerobic respiration takes over inside the muscle cells: pyruvate is converted into lactic acid instead of being fully broken down, and the build-up of this lactic acid is what causes cramps.
(D) 2 marks Name the balloon-like structures in the lungs where gas exchange actually takes place, and explain one feature that makes them efficient at this job.
Answer: These structures are called alveoli. They are efficient because their walls carry an extensive network of blood vessels right against the air inside them, and because there are a very large number of them, giving a huge total surface area for oxygen and carbon dioxide to be exchanged quickly.
(A) 1 mark What is this machine called, and what process does it use to clean the blood?
Answer: The machine is called an artificial kidney, and it cleans the blood using a process called dialysis.
(B) 1 mark What must the dialysing fluid contain, or not contain, for this process to work?
Answer: The dialysing fluid must have the same osmotic pressure as blood, but must not contain any nitrogenous waste.
(C) 2 marks Explain how waste actually leaves the patient’s blood inside the machine.
Answer: As the patient’s blood passes through the semi-permeable tubes, waste products diffuse out of the blood into the dialysing fluid, because the fluid itself contains none of these wastes; the purified blood is then pumped back into the patient’s body.
(D) 2 marks Name one important way this machine’s function differs from how a real kidney works.
Answer: A real kidney selectively re-absorbs useful substances, such as glucose, amino acids, salts and most of the water, back into the blood as filtrate flows along the nephron’s tubule. This artificial process involves no such re-absorption at all.