Question:
Formulate a hypothesis regarding which of these extra structures are needed in the cells below so they can perform their functions:
a) Cells forming the lining of the small intestine, where digested foods are absorbed.
▶️Answer/Explanation
Ans: Microvilli, vesicles, pseudopodia.
b) White blood cells that fight disease by moving into infected tissue and engulfing the organisms causing the infection.
▶️Answer/Explanation
Ans: Lysosomes, actin and myosin filaments, pseudopodia.
c) Neurons that transmit nerve impulses and send signals across synapses from one neuron to another.
▶️Answer/Explanation
Ans: Vesicles.
d) Cells that develop into hair or nail.
▶️Answer/Explanation
Ans: Keratin fibres, microtubules.
Question:
The photos (I–IV) shown here are electron micrographs of the four cell types in the previous question. Apply your scientific knowledge to deduce the cell type in each photo and what cell structures are visible.
▶️Answer/Explanation
Ans: I is nerve endings/synapses in a neuron.
II is a white blood cell that has engulfed disease–causing microbes.
III is a cell that is developing into cornified skin.
IV is cells in the lining of the small intestine that absorb digested food.
Question:
Which features (I–V) help cheek lining cells to perform various functions (a–d)?
I. They are very thin cells that overlap adjacent cells.
II. They are flat cells with a thin flattened nucleus.
III. Their cell membrane is impermeable to most substances.
IV. They are easily rubbed off, so the cheek lining is replaced every day or so.
V. They contain keratin which is a tough fibrous protein.
a. Protecting the mouth from damage by acids and other chemicals in food
▶️Answer/Explanation
Ans: Protection against acid/chemicals is helped by features I and III.
b. Providing a smooth surface inside the mouth so food can be moved easily during chewing
▶️Answer/Explanation
Ans: Smooth surface is helped by I and II.
c. Protecting the mouth from damage by hard foods when they are chewed
▶️Answer/Explanation
Ans: Protection against hard foods is helped by IV and V.
d. Preventing bacteria in the mouth from causing an infection by getting into cheek tissues
▶️Answer/Explanation
Ans: Preventing bacterial infection is helped by III and V.
Question:
Explain the reasons for a different receptor being needed for every hormone and neurotransmitter.
▶️Answer/Explanation
Ans: Every hormone/neurotransmitter has a different molecule/structure/form; specific receptors avoid confusion between different hormones/neurotransmitters.
Question:
Explain whether neurotransmitters or hormones have a more rapid effect on the body.
▶️Answer/Explanation
Ans: Neurotransmitters have a more rapid effect than hormones; because they only have to cross a synapse; whereas hormones have to be carried around the blood stream; and neurons initiate
impulses very rapidly after receiving a neurotransmitter.
Question:
Explain whether neurotransmitters or hormones have a more widespread effect on the body.
▶️Answer/Explanation
Ans: Hormones have a more widespread effect; because the blood stream carries hormones every–where in the body; whereas neurotransmitters only convey a message across one synapse.
Question:
Every receptor has a special site to which only certain molecules can bind. Which other group of proteins has a binding site to which specific molecules bind?
▶️Answer/Explanation
Ans: Enzymes are another group; they have an active site; to which specific substrates/reactants bind.
Question:
Proteins such as receptors have functions. Does anything smaller than a protein molecule have a function within the human body?
▶️Answer/Explanation
Ans: Depends on our understanding of function; we have to consider the differences between functions, purposes and roles; debatable whether small molecules such as glucose have an inherent
function or are used by living organisms for a purpose; calcium ions are used as messengers in muscle/neurons which is a function; perhaps a molecule/ion must have a specific role (in all
organisms) for this to be its function.
Question:
The researchers have discovered the functions of 324 genes in JCVI-Syn-3.0. Calculate the percentage of the genes in this synthetic bacterium that currently have an unknown function.
▶️Answer/Explanation
Ans: [(473 – 324)/473] × 100% = 31.5%
Question:
Explain how the researchers could discover whether a gene was needed for the bacterium to survive and reproduce successfully in the laboratory.
▶️Answer/Explanation
Ans: Eliminate a gene artificially; attempt to culture the microbe lacking the gene; if the gene isn’t vital the bacterium will grow and multiply to form a visible colony.
Question:
Discuss whether the 473 genes in JVCI- Syn-3.0 must all have a function.
▶️Answer/Explanation
Ans: Each of the 473 genes is vital; implying that they all have a function.
Question:
Naturally occurring bacteria have more than 473 genes. For example, Mycoplasma mycoides taken from its natural habitat in the stomach of cattle has about 900 genes. Is it reasonable to expect none, all or some of these extra genes to have a function?
▶️Answer/Explanation
Ans: Some of the extra genes might be needed to cope with different/varying conditions; a gene that has lost its function would presumably be eliminated eventually; but this might take a long time if the disadvantage of having an extra gene was small; extra genes give variation; so allow evolution; so there may be benefits in having extra genes even if they do not currently have a function.
Question:
What are the advantages of specializing in one function?
▶️Answer/Explanation
Ans: Perform the function more efficiently.
Question:
What are the advantages of performing a wide range of functions?
▶️Answer/Explanation
Ans: Fewer cell types/organs needed; less communication/coordination needed; less transport needed.
Question:
What examples of specialists and generalists can you find in the wider world?
▶️Answer/Explanation
Ans: Supermarket/superstore sells many different types of goods; greengrocer sells only fruits and vegetables.
Question:
What is the advantage of having separate functions performed in separate compartments?
▶️Answer/Explanation
Ans: Conditions can be kept ideal for one specific function; one process cannot interfere with another; mutually incompatible functions can be performed at the same time.
Question:
What is the advantage of having many small compartments which carry out the same function, rather than one large compartment?
▶️Answer/Explanation
Ans: Back–up; if one compartment fails there should still be other ones working.
Question:
What is the advantage of having all functions carried out in one undivided space?
▶️Answer/Explanation
Ans: Less movement/transport needed between compartments.
Question:
What examples can you find in the wider world of open-plan organization and division into silos.
▶️Answer/Explanation
Ans: Bees store honey is cells rather than in one undivided space; main concourse of Grand Central Terminal in New York as a large open–plan space.
Question:
Discuss the reasons for the type of organization seen in these photos.
▶️Answer/Explanation
Ans:
- Oil is stored in multiple tanks rather than one large tank at a refinery so different types of oil can be kept separate; so failure of one tank has less catastrophic consequences; because smaller tanks are structurally stronger.
- Enclosed fields allow grazing to be controlled more precisely; allow fields to be set aside for hay/silage making; open hill grazing involves less work in moving stock; allows stock to find the best grazing themselves; allows stock to move in response to weather conditions; allows stock to spread out more/develop territories.
- Cells in a penitentiary protect prisoners from each other; make it easier to control prisoners; give prisoners more privacy.
- Open dormitories in a pilgrim’s hostel allow the maximum number of pilgrims to be accommodated; discourage impropriety.
Question:
Compare the TPN and FDA diets by giving three similarities.
▶️Answer/Explanation
Ans: Carbohydrates are the main component; lipids are the second largest component; vitamins/mineral elements are included.
Question:
Explain the differences between TPN and FDA-recommended diet in:
a) starch
▶️Answer/Explanation
Ans: Starch in FDA diet but not TPN.
b) amino acids
▶️Answer/Explanation
Ans: Amino acids in TPN but proteins in FDA diet.
c) vitamins
▶️Answer/Explanation
Ans: More vitamins in FDA diet than TPN.
d) dietary fiber.
▶️Answer/Explanation
Ans: Dietary fibre in FDA diet but not in TPN.
Question:
The TPN fluid must be sterile but this is not necessary with food ingested by mouth. What is the reason for this difference?
▶️Answer/Explanation
Ans: Bacteria in food ingested by mouth are killed by stomach acid; bacteria in TPN fluid entering into a vein would cause septicemia/infection of the blood.
Question:
Suggest three conditions that might result in a patient in hospital needing TPN.
▶️Answer/Explanation
Ans: Gut surgery which stops the intestines from working; ulcerative colitis where absorption is ineffective; blockages to the intestines; coma; chronic diarrhea.
Question:
Of the 20 amino acids used to make proteins by human cells, 12 are usually included in TPN. How can the other 8 amino acids be obtained if they are not included in the diet?
▶️Answer/Explanation
Ans: Non–essential amino acids are made by conversion from other amino acids.
Question:
Discuss whether nutrients such as amino acids have a function in cells or are merely needed.
▶️Answer/Explanation
Ans: Debatable – depends on meaning of ‘function’; amino acids are naturally occurring substances; which living organisms use to provide a range of chemical properties in proteins.
Question:
For each of the 10 functions in the table, find out which organ or organs performs it.
▶️Answer/Explanation
Ans:
- Absorption of digested foods – small intestine;
- Absorption of water – colon;
- Chewing of food – mouth cavity;
- Digestion of starch in neutral conditions – mouth cavity and small intestine;
- Digestion of lipids in neutral conditions –small intestine;
- Digestion of proteins in acid conditions –stomach;
- Digestion of proteins in neutral conditions –small intestine;
- Killing bacteria – stomach;
- Temporary storage of food – stomach;
- Swallowing and vomiting – esophagus.
Question:
When you have assigned each function to an organ, deduce the sequence in which the functions are performed as food passes through the digestive system.
▶️Answer/Explanation
Ans: 1) Chewing of food
2) Swallowing
3) Killing bacteria and digestion of proteins in acid conditions
4) Temporary storage of foods
5) Digestion of proteins, lipids and starch in neutral conditions
6) Absorption of digested foods
7) Absorption of water
Question:
Try to explain the reasons for the sequence in which the functions of the digestive system are performed.
▶️Answer/Explanation
Ans: Food has to be chewed first so it is small enough to swallow; swallowing gets food through the thorax to reach the abdomen where most of the digestive system is located; important to kill bacteria (with acid) near the start; acid hydrolysis of protein can be carried out at the same time; digestion of other macromolecules can then be accomplished with suitable gut flora; followed by absorption of digested foods; and then absorption of water.
Question:
Discuss whether there are any organs in the digestive system that have:
a) the same functions as each other
▶️Answer/Explanation
Ans: Mouth cavity and small intestine both used for digestion of starch; salivary glands and pancreas both produce amylase.
b) no functions at all.
▶️Answer/Explanation
Ans: Appendix has no (clear/discovered) function.
Question:
Identify these organs:
a) the organ colored red and the green organ adjacent to it
▶️Answer/Explanation
Ans: Liver (red); gall bladder (green).
b) the two bright yellow organs.
▶️Answer/Explanation
Ans: Kidneys.
Question:
Bone tissue is shown pale yellow on this CT scan. Identify the five bones that are visible.
▶️Answer/Explanation
Ans: One vertebra (lower centre) four ribs (near body surface in lower half of scan).
Question:
The small intestine is visible in the centre and right of the CT scan. Describe and explain its appearance in the scan.
▶️Answer/Explanation
Ans: Many separate circular or ovoid sections; intestine is a tubular structure which twists and turns so passes through the plane of the scan repeatedly.
Question:
Muscle tissue has the same appearance wherever it occurs in the scan. Identify four organs with muscle tissue that are visible.
▶️Answer/Explanation
Ans: Intercostal muscle (between the ribs); wall of intestine; back muscle/muscle for bending or straightening the back; diaphragm; abdomen wall/rectus muscle.
Question:
Which groups of animals develop a head and which do not?
▶️Answer/Explanation
Ans: Insects, birds and mammals are examples of groups with a head; sea anemones, flatworms and sponges are examples of animal groups without a head.
Question:
What is the function of a head?
▶️Answer/Explanation
Ans: The head is a region where co–ordination happens, with a concentration of sense organs providing in– puts, a relatively large body of nerve tissues in the form of a brain or cerebral ganglia, many synapses between neurons; also a mouth for ingestion of food.
Question:
Discuss the reasons for the main sense organs being located in the head.
▶️Answer/Explanation
Ans: Anterior/highest/most protruding part of body; close to mouth; sense organs can be grouped together in the ideal position for sensation; short distance for impulses to pass from sense organs to brain/CNS/cerebral ganglia.
Question:
Suggest disadvantages of sense organs being located elsewhere in the body.
▶️Answer/Explanation
Ans: Longer distance for impulses to travel to brain/ CNS/cerebral ganglia; less useful for coordinating eating/ingestion; further from eye/other sense organs so not as easy to combine sensory inputs.
Question:
Rods and cones are useful at different times. When are rods and cones most useful?
▶️Answer/Explanation
Ans: Rods are most useful in dim light; at dawn and dusk; at night; cones are most useful in bright light; most useful for producing detailed/high definition images.
Question:
Rods and cones are not distributed evenly through the retina. Where are there most rods and most cones?
▶️Answer/Explanation
Ans: Most cones in the fovea/yellow spot/centre of retina; most rods around/close to (but not in) the fovea.
Question:
Rods and cones form a tissue layer in the retina but there are many other tissues in the eye. What is the function of these other tissues? Would it be possible to have the sense of vision without any of them?
▶️Answer/Explanation
Ans: Iris controls the amount of light passing through the pupil into the eye; cornea refracts light to help produce a focused image; pupil allows light to pass into the eye; ciliary muscle controls the shape of the lens; lens adjusts the amount of refraction to focus an image on the retina; suspensory ligaments transmit tension to the lens; vision would be much poorer without these other
tissues.
Question:
What is the difference between a sensory receptor and a sense organ?
▶️Answer/Explanation
Ans: Sensory receptor is a cell type that detects a stimulus; sense organ contains receptor cells; and other tissues to help the receptors to function effectively.
Question:
Find each of these structures in the photograph of the baby and then draw a labelled sketch diagram to show their relative positions: pupil, iris, sclera, opening of tear (lacrimal) gland ducts, eyelashes, eyelid and eyebrow.
▶️Answer/Explanation
Ans: Drawing should consist of sharp, continuous, easily visible lines; the seven structures should each be indicated by a clear ruled labelling line and the name.
Question:
What is the reason for the pupil appearing black?
▶️Answer/Explanation
Ans: No light emerges from the eye through the pupil so it appears black; there is a tissue called the choroid behind the retina that absorbs any light passing unabsorbed through the retina;
preventing reflection back out through the pupil.
Question:
Explain where the baby was when the photo was taken—in a brightly illuminated or dimly lit room.
▶️Answer/Explanation
Ans: Brightly illuminated room; the pupils are constricted; the reflection of a fluorescent strip light can be seen in the baby’s corneas.
Question:
Blue eyes are common in some human populations but are absent from others. Identify some parts of the world where all of the indigenous population has brown eyes and explain the reasons for this.
▶️Answer/Explanation
Ans: Brown eyes in Africa/India/South East Asia; where there is high intensity sunlight; so brown irises are needed to protect the retina from excessive light.
Question:
Muscles in the eyelids allow the eye to be closed. When does the eye close and what are the reasons for closure?
▶️Answer/Explanation
Ans: Eye closes when we are asleep; when we do not use our vision; and closing the eye protects it while we are unconscious; eyes close when we blink; to lubricate the eye; when dust/dirt/insects/foreign bodies have got onto the cornea/conjunctiva; to clear foreign bodies off the surface of the eye; eye closes if an insect approaches; to prevent it from entering the eye.
Question:
There are eyelashes above and below the eye, but an eyebrow only above it. Suggest hypotheses to explain where the eyelashes and eyebrow are located.
▶️Answer/Explanation
Ans: Eyelashes help to prevent foreign bodies from getting into the eye; eyebrow stops sweat from running down into the eye from the forehead.
Question:
What are the advantages of having two eyes rather than just one? You could formulate a hypothesis in answer to this question and then design an experiment to test your hypothesis.
▶️Answer/Explanation
Ans: Gives stereoscopic vision; allows depth/distance/perspective to be judged; allows the size of objects to be judged.
Question:
a) What is the sequence of structures through which sound waves pass from the air outside until they are dissipated inside the ear?
▶️Answer/Explanation
Ans: Outer ear; ear drum; middle ear; ossicles in middle ear; oval window; cochlea; round window.
b) Discuss whether the sound waves are passing through a solid, liquid or gas at each stage in this sequence.
▶️Answer/Explanation
Ans: Outer ear is gas–filled; ear drum is solid; ossicles in middle ear are solid; oval window is solid; cochlea is liquid; round window is solid.
Question:
Explain the functions of the round and oval windows.
▶️Answer/Explanation
Ans: Oval window allows sounds to pass from the ossicles/middle ear into the cochlea; oval window helps to amplify sounds; round window carries out compensatory movements; to allow the fluid in the cochlea to vibrate; because fluids are incompressible.
Question:
The loudness of a sound is due to the amplitude of the sound waves. How are we able to hear sounds with low amplitude and also avoid ear damage from sounds with high amplitude?
▶️Answer/Explanation
Ans: Middle ear amplifies the sound; by the arrangement of the ossicles; by the oval window being smaller than the ear drum; muscles can move the ossicles when sound is loud; to reduce the transmission of sound through them.
Summative assessment
Food in the gut
Question:
Cystic fibrosis (CF) is the most common genetic disease in Canada, the United States of America and north-west Europe. Chloride channels in certain cells do not function resulting in very viscous mucus that causes lung problems and blocks the pancreatic duct.
a) State the function of the pancreatic duct.
▶️Answer/Explanation
Ans: Carries pancreatic juice/enzymes secreted by the pancreas to the small intestine.
A percentile (centile) is a measure used to indicate the value below which a given percentage of observations in a population occur. For example, 50% of people in the population have a height lower than the 50th percentile. The bar chart (right) shows the percentage of female CF patients in the United States and Canada that are in each of six different height percentile classes. If their heights matched the distribution for the general population, then 25% of them would be above the 75th percentile.
b) Using the US data in the bar chart, deduce the effect of CF on growth.
▶️Answer/Explanation
Ans: Reduces growth; more than 25% of CF patients are below the 25th percentile; fewer than 25% of CF patients are above the 75% percentile.
c) Suggest reasons for the effect of CF on growth.
▶️Answer/Explanation
Ans: Less secretion of enzymes from the pancreas into the small intestine; less digestion of foods/protein/starch/lipids; less digested food absorbed/carried to cells by the blood stream; more respiratory tract infections.
d) The data suggests that where a CF patient lives affects their chance of growing at a normal or a reduced rate. Deduce where in North America patients seem to have a higher chance of normal growth rates and suggest possible reasons for this.
▶️Answer/Explanation
Ans: Canada; because the reductions in growth shown by the percentile data are less; better treatment of CF patients by the Canadian than US health care systems; enzyme replacement capsules; better diet; better treatment of respiratory infections.
Question:
Some patients have an ileostomy bag fitted. Material from the gut can pass into it at the end of the small intestine. An opening (stoma) through the abdomen wall is created surgically and the bag is connected to this and concealed under clothing.
a) Suggest one reason for fitting an ileostomy bag.
▶️Answer/Explanation
Ans: Colon removed due to cancer.
b) Compare the functions of an ileostomy bag and the large intestine by giving one similarity and one difference.
▶️Answer/Explanation
Ans: Both receive wastes from the small intestine; colon absorbs water from the wastes and returns it to the blood stream but ileostomy bag does not.
c) What change in diet would you recommend to a patient after they have had an ileostomy bag fitted?
▶️Answer/Explanation
Ans: Less fibre in diet (initially); drink plenty of fluid to replace water losses; vitamin supplement/vitamin B12 which is mostly made in the colon; avoid foods that cause flatulence/dietary gas; avoid fizzy/carbonated drinks.
d) What change in the volume of urine would you expect after the fitting of an ileostomy bag?
▶️Answer/Explanation
Ans: Smaller volume of urine because of water losses to the ileostomy bag
Investigating food absorption
Dialysis tubing is manufactured for use in kidney machines. It can be used to simulate absorption of food by diffusion in the gut, because it is similar in permeability. The diagram shows how such a simulation could be contrived.
Possible foods to test:
The presence of such foods can be detected using these methods:
● glucose—with urine test strips or with Benedict’s test
● starch—with the iodine test
● amino acids—with universal indicator or a pH probe
● casein—with the biuret test.
Question:
Formulate a hypothesis for the function of the gut (to digest food) and explain it using scientific reasoning.
▶️Answer/Explanation
Ans: Undigested food molecules are too large/insoluble; for absorption; so must be broken down into smaller/more soluble molecules.
Question:
Design an experiment to test your hypothesis, including how you will control the variables.
▶️Answer/Explanation
Ans: Design should include clear statement of independent, dependent and control variables, rationale for the method and practical details, consideration of ethics and risks, with marks awarded on a scale from 0 marks for a completely inadequate design to eight marks for an exemplary design.
Question:
Explain how you will collect data in your investigation.
▶️Answer/Explanation
Ans: Details of testing for glucose; starch; amino acids (by pH); casein/protein.
Analysis and evaluation
Question:
Present the results of your investigation in a results table.
▶️Answer/Explanation
Ans: Column headings; row headings; each result in a separate cell on the table.
Question:
Interpret the data and explain your results using scientific reasoning.
▶️Answer/Explanation
Ans: Interpretation should explain what the results show about the permeability of the membrane to larger and smaller molecules, with marks awarded on a scale from 0 marks for an incorrect/invalid interpretation to 3 marks for a convincing interpretation based on scientific reasoning.
Question:
Evaluate the validity of your hypothesis based on the outcome of your investigation.
▶️Answer/Explanation
Ans: Evaluation should state clearly whether the results actually obtained falsify the hypothesis or provide evidence in support of it, together with an assessment of the strength of the evidence, awarding marks on a scale from 0 marks for an incorrect/invalid evaluation to 3 marks for a convincing evaluation based on the results of the investigation.
Question:
Evaluate your method. Was it a valid test of your hypothesis?
▶️Answer/Explanation
Ans: Evaluation should state clearly to what extent the method allowed the hypothesis to be tested fully, partially tested or not tested at all, with marks awarded on a scale of 0 marks for an incorrect/invalid evaluation to 3 marks for a convincing evaluation of the method.
Question:
Explain how you could extend or improve your method.
▶️Answer/Explanation
Ans: Marks should be awarded on a scale from 0 marks for trivial/invalid/impractical suggestions to 3 marks for a convincing explanation of two or more extensions/improvements.
Researching the risks of GM foods
The following text is from Netherwood, T. et al. 2004. Nature Biotechnology. Vol 22. Pp 204–209. Read the passage and work through the tasks that follow.
Question:
a) Explain why it was essential for scientists to get permission from the volunteers before carrying out this research.
▶️Answer/Explanation
Ans: Informed consent always needed; unethical to carry out procedures without permission; volunteers must be aware of any potential risks/issues; and have given permission knowing about these risks/issues.
b) Few scientists consider the ingestion of new genes in GM foods to be a significant risk. Explain why research into this issue is still worthwhile.
▶️Answer/Explanation
Ans: To convince others that ingestion of new genes in GM foods is not a risk; because the scientists might be wrong in thinking that the procedure is safe; because some risks are unexpected; because the precautionary principle states that those introducing a new procedure have a duty to demonstrate that it is safe.
c) Explain the conclusions that can be drawn about what happens to the DNA of the epsps gene as it passes through the small and large intestines.
▶️Answer/Explanation
Ans: A small percentage/3.7% to 0.00001% of epsps genes passed through the gut to the end of the small intestine; 99.99999 to 96.3% of epsps genes broken down in the small intestine; all remaining epsps genes were broken down in the large intestine; feeding on GM food with epsps genes did not lead to an increase in gut bacteria carrying the epsps gene.
d) Write a brief newspaper article explaining the research into the risks of ingesting GM foods, for readers who have little biological knowledge but strong views on this subject.
▶️Answer/Explanation
Ans: Marks should be awarded on a scale from 0 marks for an account that is incomprehensible or misleading to 6 marks for an exemplary account explaining complex ideas in simple terminology and in phraseology that encourages the reader to continue to the end of the article.