Biology (9-1) 0970 | Paper 4 Mock 01 | Theory (Extended)
Question 1 Report
There are millions of kinds of living things. Scientists sort them into groups. They group them by the features they share. This sorting is called classification. It helps scientists to study the organisms. It also shows how they may be related. The largest groups are the kingdoms. There is an animal kingdom and a plant kingdom. Each kingdom is split into smaller groups. This goes on until each single type is reached. Each type is a species. Every species has a two-part scientific name. Scientists everywhere use this name. A student was asked why we classify and how the naming works.
(a) State what is meant by the term species. [1]
(b) State the name given to the largest groups into which living things are classified. [1]
(c) Explain two reasons why scientists find it useful to classify organisms. [2]
(d) The scientific name of the lion is Panthera leo. Explain how this two-part naming system works and why it is used by scientists around the world. [4]
(e) Suggest why organisms that share many features are usually placed in the same group. [2]
This question tests the reasons for classifying organisms and how the binomial (two-part) naming system works.
(a) A species is a group of organisms that can breed together to produce fertile offspring [1].
(b) The largest groups into which living things are classified are the kingdoms [1].
(c) Any two reasons classification is useful (1 each): it makes organisms easier to identify and study [1]; and it shows how organisms are related (their evolutionary relationships) [1].
(d) The binomial system, for Panthera leo: the first part (Panthera) is the genus and the second part (leo) is the species [1]; the genus name begins with a capital letter and the species name with a small letter (and the name is written in italics/underlined) [1]; the same name is used in every country and language [1]; so scientists everywhere know exactly which organism is meant, avoiding confusion from different local names [1].
(e) Organisms sharing many features are placed in the same group because they are likely to be closely related (share a recent common ancestor) [1]; so grouping them together reflects and shows this relationship [1].
Answer Details
This question tests the reasons for classifying organisms and how the binomial (two-part) naming system works.
(a) A species is a group of organisms that can breed together to produce fertile offspring [1].
(b) The largest groups into which living things are classified are the kingdoms [1].
(c) Any two reasons classification is useful (1 each): it makes organisms easier to identify and study [1]; and it shows how organisms are related (their evolutionary relationships) [1].
(d) The binomial system, for Panthera leo: the first part (Panthera) is the genus and the second part (leo) is the species [1]; the genus name begins with a capital letter and the species name with a small letter (and the name is written in italics/underlined) [1]; the same name is used in every country and language [1]; so scientists everywhere know exactly which organism is meant, avoiding confusion from different local names [1].
(e) Organisms sharing many features are placed in the same group because they are likely to be closely related (share a recent common ancestor) [1]; so grouping them together reflects and shows this relationship [1].
Question 2 Report
| Region | pH |
|---|---|
| mouth | 7 |
| stomach | 2 |
| duodenum | 8 |
| ileum | 8 |
The conditions inside the alimentary canal are not the same all the way along it. Each region has its own pH, which suits the enzymes that work there. A student used a pH probe to measure the pH of the contents of four different regions of the canal a short time after a person had eaten a meal. The results are shown in Table 9.1.
(a) State the region shown in the table that has the lowest pH. [1]
(b) Name an enzyme that works best in the conditions found in the stomach. [1]
(c) Explain how the low pH of the stomach both aids digestion and helps to protect the body. [3]
(d) Describe how the pH changes between the stomach and the duodenum, and explain how this change is brought about. [3]
(e) Name the alkaline secretion that helps to raise the pH in the duodenum. [1]
(f) Explain why enzymes that act in the duodenum would not work well at pH 2. [3]
(g) State the general term for the breakdown of large food molecules into small soluble ones. [1]
This question tests how pH varies along the alimentary canal and why each region suits its own enzymes. A pH probe reading shows that conditions change sharply from the acidic stomach to the alkaline duodenum.
(a) The region with the lowest pH is the stomach [1].
(b) An enzyme that works best in stomach conditions is pepsin [1].
(c) The low pH of the stomach both aids digestion and protects the body: the acid provides the optimum pH for pepsin, so protein digestion is fast [1]; it kills bacteria / pathogens in the food [1]; thereby protecting the body from infection [1].
(d) Between the stomach and duodenum the pH rises / becomes alkaline (from about 2 to 8) [1]; because alkaline bile and pancreatic juice enter the duodenum [1]; and these neutralise the acid from the stomach [1]. The change is a deliberate switch of conditions to suit intestinal enzymes.
(e) The alkaline secretion that raises the pH is bile / pancreatic juice [1].
(f) Duodenal enzymes would not work at pH 2 because their optimum pH is alkaline (about 8) [1]; at pH 2 the active site changes shape / the enzyme is denatured [1]; so substrate no longer fits and digestion stops [1].
(g) The breakdown of large food molecules into small soluble ones is called digestion [1].
Exam tip: connect each region's pH to the enzymes released there - acid for pepsin in the stomach, alkali for intestinal enzymes - and remember that neutralisation by bile and pancreatic juice is what drives the pH up.
Answer Details
This question tests how pH varies along the alimentary canal and why each region suits its own enzymes. A pH probe reading shows that conditions change sharply from the acidic stomach to the alkaline duodenum.
(a) The region with the lowest pH is the stomach [1].
(b) An enzyme that works best in stomach conditions is pepsin [1].
(c) The low pH of the stomach both aids digestion and protects the body: the acid provides the optimum pH for pepsin, so protein digestion is fast [1]; it kills bacteria / pathogens in the food [1]; thereby protecting the body from infection [1].
(d) Between the stomach and duodenum the pH rises / becomes alkaline (from about 2 to 8) [1]; because alkaline bile and pancreatic juice enter the duodenum [1]; and these neutralise the acid from the stomach [1]. The change is a deliberate switch of conditions to suit intestinal enzymes.
(e) The alkaline secretion that raises the pH is bile / pancreatic juice [1].
(f) Duodenal enzymes would not work at pH 2 because their optimum pH is alkaline (about 8) [1]; at pH 2 the active site changes shape / the enzyme is denatured [1]; so substrate no longer fits and digestion stops [1].
(g) The breakdown of large food molecules into small soluble ones is called digestion [1].
Exam tip: connect each region's pH to the enzymes released there - acid for pepsin in the stomach, alkali for intestinal enzymes - and remember that neutralisation by bile and pancreatic juice is what drives the pH up.
Question 3 Report
On a hot day, or during hard exercise, the body gains heat and its core temperature begins to rise. Fig. 1.1 shows a section through the skin, which contains structures that help to cool the body when it becomes too warm. Sweat glands and blood vessels in the skin change their activity to increase the loss of heat from the body surface.
(a) Name the structure, shown in the skin, that produces sweat. [1](b) State what happens to the rate of sweating when the body becomes too hot. [1]
(c) Describe how sweating helps to cool the body. [3]
(d) Describe how the blood vessels supplying the skin surface respond when the body is too hot. [2]
(e) Explain how this change in the blood vessels increases heat loss from the body. [3]
(f) Explain why a person may feel cold and start to shiver a short time after heavy sweating. [2]
(g) Suggest why sweating a lot on a hot day increases a person's need to drink water. [2]
This question is about how the skin cools the body when the core temperature rises, and the consequences of heavy sweating.
(a) Sweat is produced by the sweat gland [1] (the coiled structure deep in the dermis, shown with its duct leading to the surface).
(b) When the body becomes too hot the rate of sweating increases / more sweat is produced [1].
(c) Sweating cools the body because the sweat lies on the skin surface [1]; the water in the sweat evaporates [1]; and evaporation takes heat (latent heat) energy from the skin, cooling the body [1] [3]. The heat needed to turn liquid sweat into vapour is drawn from the skin, lowering its temperature.
(d) The arterioles supplying the skin surface widen / dilate [1]; this is called vasodilation [1] [2].
(e) Because of vasodilation, more blood flows close to the skin surface [1]; so more heat is carried to the surface [1]; and more heat is lost by radiation to the surroundings [1] [3].
(f) A person may feel cold and shiver after heavy sweating because so much water and heat has been lost that the body temperature falls below normal [1]; the body then responds by shivering to generate heat and raise the temperature back towards normal [1] [2].
(g) Sweating a lot increases the need to drink because water is lost from the body in the sweat [1]; this must be replaced by drinking to keep the water content of the blood constant (osmoregulation), otherwise the blood becomes too concentrated [1] [2].
Answer Details
This question is about how the skin cools the body when the core temperature rises, and the consequences of heavy sweating.
(a) Sweat is produced by the sweat gland [1] (the coiled structure deep in the dermis, shown with its duct leading to the surface).
(b) When the body becomes too hot the rate of sweating increases / more sweat is produced [1].
(c) Sweating cools the body because the sweat lies on the skin surface [1]; the water in the sweat evaporates [1]; and evaporation takes heat (latent heat) energy from the skin, cooling the body [1] [3]. The heat needed to turn liquid sweat into vapour is drawn from the skin, lowering its temperature.
(d) The arterioles supplying the skin surface widen / dilate [1]; this is called vasodilation [1] [2].
(e) Because of vasodilation, more blood flows close to the skin surface [1]; so more heat is carried to the surface [1]; and more heat is lost by radiation to the surroundings [1] [3].
(f) A person may feel cold and shiver after heavy sweating because so much water and heat has been lost that the body temperature falls below normal [1]; the body then responds by shivering to generate heat and raise the temperature back towards normal [1] [2].
(g) Sweating a lot increases the need to drink because water is lost from the body in the sweat [1]; this must be replaced by drinking to keep the water content of the blood constant (osmoregulation), otherwise the blood becomes too concentrated [1] [2].
Question 4 Report
The body keeps its inside conditions steady. This is true even when the outside changes a lot. This steady state is called homeostasis. One key thing that is kept steady is the body temperature. It is held near 37 degrees. If the body is too hot or too cold, its enzymes may fail. So the body can gain and lose heat. Part of the brain checks the temperature of the blood. It controls these changes. A student came in from a hot day. They were sweating. Their face was red. They were asked to explain the changes in the skin.
(a) State what is meant by the term homeostasis. [1]
(b) Name the part of the brain that monitors the temperature of the blood. [1]
(c) Explain how sweating helps to cool the body down on a hot day. [3]
(d) Explain how a change in the flow of blood to the skin helps to cool the body. [3]
(e) Describe how the body responds to being too cold in order to raise its temperature. [3]
This question tests temperature homeostasis and how the skin responds to being too hot or too cold.
(a) Homeostasis is the maintenance of a constant internal environment (steady internal conditions) [1].
(b) The part of the brain that monitors the temperature of the blood is the hypothalamus [1].
(c) Sweating cools the body because sweat is released onto the surface of the skin [1]; the water in the sweat evaporates [1]; and evaporation takes heat energy from the body, so the body cools [1].
(d) Changing blood flow to the skin cools the body by vasodilation: the arterioles supplying the skin widen [1]; so more blood flows near the surface of the skin [1]; and more heat is lost by radiation to the surroundings [1]. (Note the vessels themselves move blood nearer the surface; the capillaries do not "move".)
(e) To raise its temperature when too cold, the body responds by shivering: muscles contract rapidly, releasing heat from respiration [1]; vasoconstriction: skin blood vessels narrow so less heat is lost from the surface [1]; and less sweat is produced [1].
Answer Details
This question tests temperature homeostasis and how the skin responds to being too hot or too cold.
(a) Homeostasis is the maintenance of a constant internal environment (steady internal conditions) [1].
(b) The part of the brain that monitors the temperature of the blood is the hypothalamus [1].
(c) Sweating cools the body because sweat is released onto the surface of the skin [1]; the water in the sweat evaporates [1]; and evaporation takes heat energy from the body, so the body cools [1].
(d) Changing blood flow to the skin cools the body by vasodilation: the arterioles supplying the skin widen [1]; so more blood flows near the surface of the skin [1]; and more heat is lost by radiation to the surroundings [1]. (Note the vessels themselves move blood nearer the surface; the capillaries do not "move".)
(e) To raise its temperature when too cold, the body responds by shivering: muscles contract rapidly, releasing heat from respiration [1]; vasoconstriction: skin blood vessels narrow so less heat is lost from the surface [1]; and less sweat is produced [1].
Question 5 Report
Fig. 8.2 again shows the growth of a population that has been placed in a container with a limited supply of food. As the population becomes larger, the individuals begin to compete with one another for resources such as food and space, and waste products build up in their surroundings. These factors slow down the growth of the population and eventually stop it from increasing any further. The size of a population is controlled by the balance between the number of individuals that are born and the number that die. When these two rates become equal, the size of the population stops changing and stays roughly constant.
(a) State two resources that individuals in a growing population may compete for. [2]
(b) Describe what happens to the birth rate and the death rate as a population reaches its maximum size. [3]
(c) Explain how the build-up of waste products can limit the growth of a population. [3]
(d) Suggest one factor, other than food and waste, that could cause a natural population to stop increasing. [2]
This question is about how a population growing in a closed container reaches a limit set by its resources. The S-shaped curve in Fig. 8.2 levels off because the environment can only support so many individuals.
(a) Individuals compete for anything in limited supply. Any two of: food, space, water, light or oxygen earn the marks [2]. Competition means more individuals are sharing the same fixed amount, so each gets less.
(b) As the population nears its maximum, the birth rate falls [1] and the death rate rises [1], and growth stops when the birth rate becomes equal to the death rate [1]. When births and deaths balance, the number added each generation equals the number lost, so the total stays roughly constant. This flat part of the curve is the carrying capacity [3].
(c) Waste products build up because there is no way for them to be removed in a closed container. The chain is: waste products become toxic / poisonous [1]; the conditions become unsuitable for the organisms [1]; so more individuals die or fewer reproduce, and growth stops [1]. The key idea is cause and effect: the waste itself does not use up food, it poisons the surroundings [3].
(d) Suggest any sensible factor with a reason, for example disease spreading more easily in a crowded population [1] which increases the death rate, or predators reducing the numbers [1]. The mark for the factor and the mark for its effect together give [2].
Examination tip: when a growth curve flattens, always explain it as birth rate falling towards death rate rising, not simply as "running out of food".
Answer Details
This question is about how a population growing in a closed container reaches a limit set by its resources. The S-shaped curve in Fig. 8.2 levels off because the environment can only support so many individuals.
(a) Individuals compete for anything in limited supply. Any two of: food, space, water, light or oxygen earn the marks [2]. Competition means more individuals are sharing the same fixed amount, so each gets less.
(b) As the population nears its maximum, the birth rate falls [1] and the death rate rises [1], and growth stops when the birth rate becomes equal to the death rate [1]. When births and deaths balance, the number added each generation equals the number lost, so the total stays roughly constant. This flat part of the curve is the carrying capacity [3].
(c) Waste products build up because there is no way for them to be removed in a closed container. The chain is: waste products become toxic / poisonous [1]; the conditions become unsuitable for the organisms [1]; so more individuals die or fewer reproduce, and growth stops [1]. The key idea is cause and effect: the waste itself does not use up food, it poisons the surroundings [3].
(d) Suggest any sensible factor with a reason, for example disease spreading more easily in a crowded population [1] which increases the death rate, or predators reducing the numbers [1]. The mark for the factor and the mark for its effect together give [2].
Examination tip: when a growth curve flattens, always explain it as birth rate falling towards death rate rising, not simply as "running out of food".
Question 6 Report
Excretion is the removal of waste from the body. The waste comes from chemical reactions. Two wastes are very important. One is carbon dioxide from respiration. The other is urea. Urea is made in the liver. It forms when the liver breaks down extra amino acids. The amino acids come from protein in the diet. Carbon dioxide is removed by the lungs. Urea is removed by the kidneys in the urine. If these wastes built up, they would harm the cells. A student ate a meal rich in protein. They were asked what happens to the extra amino acids.
(a) State what is meant by the term excretion. [1]
(b) Name the organ that removes carbon dioxide from the body. [1]
(c) Explain what the liver does with the excess amino acids from a protein-rich meal. [3]
(d) Explain why urea must be removed from the body. [2]
(e) Name the organ that removes urea from the blood and describe how the urea leaves the body. [3]
(a) Excretion is the removal from the body of the toxic waste products of metabolism / chemical reactions [1] (for example carbon dioxide and urea). It is different from egestion of undigested food.
(b) The organ that removes carbon dioxide is the lungs [1].
(c) With excess amino acids the liver breaks down the extra amino acids [1] in a process called deamination [1], which forms urea (from the amino part), while the rest can be used for respiration/energy [1]. The body cannot store extra amino acids, so the surplus must be dealt with.
(d) Urea must be removed because it is toxic / poisonous [1], so if it built up in the blood it would damage cells and harm the body [1].
(e) The organ that removes urea from the blood is the kidney [1]; the urea passes (dissolved in urine) down the ureter to the bladder [1], where the urine is stored before being released from the body through the urethra [1].
Answer Details
(a) Excretion is the removal from the body of the toxic waste products of metabolism / chemical reactions [1] (for example carbon dioxide and urea). It is different from egestion of undigested food.
(b) The organ that removes carbon dioxide is the lungs [1].
(c) With excess amino acids the liver breaks down the extra amino acids [1] in a process called deamination [1], which forms urea (from the amino part), while the rest can be used for respiration/energy [1]. The body cannot store extra amino acids, so the surplus must be dealt with.
(d) Urea must be removed because it is toxic / poisonous [1], so if it built up in the blood it would damage cells and harm the body [1].
(e) The organ that removes urea from the blood is the kidney [1]; the urea passes (dissolved in urine) down the ureter to the bladder [1], where the urine is stored before being released from the body through the urethra [1].
