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2I Excretion
Time: 1 hour 6 minutes
Total marks available: 66
Total marks achieved: ______
Andy Todd
Q1.
One of the characteristics of living organisms is the ability to respond to a change in
their surroundings.
In mammals, such as humans, responses are controlled by nervous or hormonal communication.
(a) ADH is an example of a hormone.
(i) Where is ADH produced?
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(ii) Describe the effects of ADH in the body.
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(b) Describe two ways in which nervous communication differs from hormonal communication.
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(c) Plants are also able to respond to their surroundings. The diagram shows young
cereal shoots (coleoptiles) which are placed in different light conditions.
Complete the diagram to suggest how each of the shoots would appear after two days.
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(d) Plant roots also respond to external stimuli.
Describe the response of roots to gravity and explain how this response benefits
the plant.
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(Total for question = 12 marks)
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Q2.
(a) The table lists some structures that provide a large surface area for the diffusion
of substances.
Complete the table by naming the organ in which each structure is found.
The first one has been done for you.
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(b) What is meant by the term diffusion?
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(c) The nephron is involved in the removal of substances from the blood.
Describe how substances are removed from the blood into the nephron.
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(Total for question = 7 marks)
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Q3.
The skin is an organ of homeostasis and excretion.
(a) Describe what is meant by the term excretion.
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(b) The diagram shows a section through the skin with two structures labelled A and B.
The structures labelled A and B play a part in homeostasis when a person enters a
very warm environment.
(i) Explain the role of structure A.
This text is an indented paragraph that lines up with the text after the "i)".
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(ii) Explain the role of structure B.
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(c) Some hormones are involved in homeostasis.
(i) Explain the role of insulin in homeostasis.
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(ii) Explain the role of ADH in homeostasis.
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(Total for question = 13 marks)
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Q4.
The human kidney removes urea from the blood.
(a) Name two other substances the kidney removes from the blood.
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(b) The diagram shows a simple kidney machine that uses dialysis to remove urea
from the blood.
Dialysis allows small molecules to be removed from the blood. This is done by
passing the dialysis solution over the tube containing the blood. The small molecules
move from a region of high concentration to a region of low concentration.
(i) Give one way in which dialysis is similar to diffusion.
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(ii) Give one way in which dialysis is similar to osmosis.
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(iii) Describe how the kidney machine removes urea from the blood.
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(iv) Another function of the kidney machine is to maintain normal blood glucose
concentration.
Suggest how the concentration of glucose in the dialysis solution helps to
maintain a normal glucose concentration in the blood.
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(v) Describe two processes that take place in the kidney but not in the kidney
machine.
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(c) Kidney failure can be treated by transplanting a healthy donor kidney into the
patient.
(i) The procedure involves connecting two blood vessels and a tube to the
transplanted kidney.
Name the two blood vessels and the tube.
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(ii) Suggest why the transplanted kidney is placed in the lower abdomen instead
of in the kidney's usual location.
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(Total for question = 16 marks)
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Q5.
The diagram shows some of the blood vessels and a nephron in the human kidney.
The numbers represent the concentration of glucose at various places in the blood
vessels and in the nephron, in arbitrary units.
(a) Explain how the structure of the blood vessels entering and leaving the glomerulus
help to move glucose into the Bowman's capsule.
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(b) What type of blood vessels are found in the glomerulus?
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(c) (i) Describe how glucose is reabsorbed from the nephron back into the blood.
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(ii) Suggest why glucose needs to be returned to the blood.
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(Total for question = 7 marks)
Andy Todd
Q6.
(a) The diagram shows a section through a leaf.
(i) Name the structures labelled A and B.
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(ii) Give the function of the waxy cuticle.
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(iii) Some of the leaf cells carry out photosynthesis. Write a word equation for this
process.
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(iv) Plants, like all living organisms, need to excrete waste products.
Explain how the excretory product of photosynthesis is removed from the
leaf.
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(b) Some plants lose their leaves in cooler months. This can be described as an
excretory mechanism. Suggest two other reasons why some plants lose their
leaves in cooler months.
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(c) Name one excretory organ in humans and name the substance it excretes.
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(Total for question = 11 marks)
Q1.
In this question candidates needed to recall where ADH is produced. Most
candidates stated the pituitary glands and some the hypothalamus. On this
occasion at International GCSE we were prepared to accept the site of release
and the site of production. In part (a) (ii) candidates had to describe the
effects of ADH on the body. The best responses described how ADH increases
the permeability of the collecting duct wall. This leads to more water being
reabsorbed into the blood by osmosis resulting in a smaller volume of more
concentrated urine being released. Some candidates tried to describe the effect
of less ADH and generally confused themselves.
In part (b) most could recall two differences between nervous and hormonal
communication. In part (c) candidates had to predict the outcome of an
experiment on coleoptiles and light. Almost all could draw the correct response
for the light from all around and most for unidirectional light few gained the mark
for coleoptile in darkness. In (d) most candidates could describe the response of
roots as positively geotropic and helping the plant by absorbing water and
mineral ions. Fewer mentioned the role of the roots in anchoring the plant.
Q2.
This question gave candidates a table of structures that provide a large surface
area for diffusion. Almost all could identify the organs correctly. In part (b) most
could describe diffusion as the movement of particles down a concentration
gradient but less able candidates wrote about substances moving rather than
ions, particles or molecules. In (c) the best responses included the movement of
molecules from the glomerulus into the Bowman's capsule under pressure.
Q3.
For this question the better students are fully aware that excretion involves the removal of
metabolic waste from the human body and gained full marks. Many gave named metabolic waste
products and many confused excretion with egestion. Most appreciated that the labelled part A in
the diagram of a skin section was a sweat gland. Marks were given for appreciating that released
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sweat will help the body lose heat when it evaporates. Weaker students struggled to interpret the
diagram and wrote about part A as if it were a hair follicle or a receptor. Most recognised part B
in the diagram and the best students gained all three marks by discussing the role of vasodilation
allowing more blood to reach the skin surface and how this would help in cooling the body.
Weaker students believed that the blood vessels move closer to the skin surface. Part (c)
examined knowledge about the role of insulin. Students are encouraged to be precise with their
language. Marks were given if students stated clearly that insulin reduces blood glucose by
converting it to glygogen which is stored in the liver. Correct spelling of glycogen was essential
as there were many answers where the term glucagon was used and examiners needed to be
confident that the students knew the difference. The role of ADH in osmoregulation is well known
by students. Marks were awarded for appreciating that ADH increases the permeability of the
collecting duct so water can be reabsorbed into the blood.
Q4.
This question concerned the kidney and use of a dialysis machine. In part (a)
most candidates could name one substance removed by the kidney. This
question sought to examine the ability of students to apply biological
principles to an unfamiliar context and therefore discriminated well between
candidates. . In part (b) (i) and (ii) candidates had to give one way that
dialysis is similar to diffusion and one way in which dialysis is similar to
osmosis. Most could describe dialysis and diffusion as being down a
concentration gradient and many could also recognise the presence of a
partially permeable as being common to dialysis and osmosis. In part (iii)
the better candidates could explain how urea is removed from the blood by
diffusion down a concentration gradient and across a partially permeable
membrane. In part (iv) only the candidates with higher levels of
understanding could suggest how the concentration of glucose in the
dialysis fluid maintains the blood glucose level. In part (v) the best
responses could describe ultrafiltration and selective reabsorption as
processes that occur in the kidney but not in the dialysis machine. Part (c)
(i) asked candidates to recall the blood vessels and the tube that are
connected to a kidney. Many could name the blood vessels but some
confused urethra with ureter or attempted an amalgam of the two. Finally,
in part (c) (ii) only the most able could suggest that the transplanted kidney
is placed in the lower abdomen as the kidney will be nearer the bladder, the
ureter and blood vessels can be shorter and access is easier.
Q5.
In this question only the best students were able to access part (a) of this question fully. Few
recognised that the difference in the diameter of the afferent and efferent arterioles is responsible
for the pressure needed for ultrafiltration, and many students gave irrelevant answers concerning
capillary structure and diffusion. In part (b), most recalled that the blood vessels of the
glomerulus are capillaries. In part (c), only the better students were able to gain full marks, no
doubt understanding that the numbers on the diagram indicate the involvement of active
transport. Most appreciated in part (d) the importance of glucose as a substrate for respiration.
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Q6.
This question provided a diagram of a section through a leaf. In part a)
almost all candidates could correctly name the structures labelled. Most
were able to give the function of the waxy cuticle as reducing transpiration
and preventing entry of microorganisms. Most could also give the word
equation for photosynthesis, although a significant minority chose to give
chemical formulae. In the final part the better candidates gained full credit
for explaining that oxygen exits the stomata down a diffusion gradient from
a high concentration to a lower one outside the leaf. Part b) asked
candidates to suggest reasons why some plants lose their leaves in cooler
months. Answers that gained credit included reduction of water loss, lack of
sunlight for photosynthesis and conservation of energy resources.
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Q1.
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Q2.
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Q3.
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Q4.
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Q5.
Q6.
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