key concepts in biology sample exam questions and answers Flashcards
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What part of a cell controls what enters and exits?
Cell membrane
What process involves the movement of water across a membrane?
Osmosis
Which type of cells is prokaryotic?
Bacterial
Describe the structure of a generalised animal cell. [4 marks]
Answer (four from):
- the cytoplasm is made from water and is where cellular reactions occur
- the nucleus contains genetic material which controls the cell
- the membrane controls the movement of molecules into and from the cell
- mitochondria are the site of respiration
- ribosomes are the site of protein synthesis
Describe the structure of a generalised plant cell. [4 marks]
Answer (four from):
- the cytoplasm is made from water and is where cellular reactions occur
- the nucleus contains genetic material which controls the cell
- the membrane controls the movement of molecules into and from the cell
- mitochondria are the site of respiration
- ribosomes are the site of protein synthesis
- the cell wall is made from cellulose and provides support
- photosynthesis occurs in chloroplasts
- cell sap is stored in the permanent vacuole
What conditions can denature an enzyme? [2 marks]
- high temperatures
- extreme (very high or low) pH
Describe the structure of a prokaryotic cell. [4 marks]
Answer (four from):
- all bacteria possess prokaryotic cells
- they do not have a nucleus
- instead their DNA is present in the cytoplasm
- the cytoplasm is made from water and is where cellular reactions occur
- the membrane controls the movement of molecules into and from the cell
- flagella rotate or move like whips to move bacterial cells
- a cell wall provides protection
Describe the differences between light and electron microscopes. [3 marks]
Answer (three from):
- light microscopes are lower magnification
- they are also lower resolution
-light microscopes can study living cells but electron microscopes cannot
- electron microscopes are more expensive
- transmission electron microscopes look at cross sections of samples
-scanning electron microscopes look at samples in three dimensions
Describe where enzymes of the digestive system are produced. [3 marks]
- carbohydrase enzymes are produced in the mouth, pancreas and small intestine
- lipase enzymes are produced in the pancreas and small intestine
- protease enzymes are produced in the stomach, pancreas and small intestine
What is the total magnification of a light microscope with an eyepiece lens of ×10 and an objective lens of ×40? [1 mark]
10 × 40 = ×400
Total magnification of microscope = magnification of eyepiece lens × magnification of objective lens
How many orders of magnitude exist between an ant which is 3 mm long and a human hair which has a diameter of 100 μm? [3 mark]
Ant = 3 mm which is 0.003 m or 10−3 m
Human hair = 100 μm which is 0.0001 or 10−4 m
So there is one order of difference.
If a drawing of a cell in a textbook is 1 cm and the scale shows it to be 0.1 mm in real life, what is its magnification? [2 mark]
1 cm = 10 mm
So, 10 mm ÷ 0.1 mm = ×100
Describe how you would make a light microscope slide of a human cheek cell. [4 marks]
Answer (four from):
- put a small drop of water on the microscope slide
- gently swab the inside of your mouth with a clean cotton bud
- the cotton bud should be disposed of into alcohol, used end down
- gently rub the cotton bud in the drop of water
- cover the sample with a glass cover slide
- if stained with methylene blue the nucleus will appear blue
- dispose of the slide into disinfectant
Describe how you would use a light microscope to view a slide. [4 marks]
Answer (four from):
- rotate the objectives so that the low power, eg ×10, is in line with the stage
- turn the coarse focus to give space between the stage and the objective lens
- place the microscope slide on the stage
- line it up so that the specimen is in the centre of the stage, where the light passes through
- focus the slide by turning the coarse focus adjustment
- draw a low power image
- rotate the objectives so that the high power objective, eg ×40, is in line with the stage
- bring the slide back into focus using the fine focus adjustment
You have just completed a practical into the effects of temperature of the rate of an enzyme reaction. Describe the graph of results you would expect. [3 marks]
- as the temperature increases so does the rate of reaction
- this will continue until the optimum temperature is reached
- at this point the enzyme’s rate of reaction is highest
- further increases in temperature will reduce the rate of reaction
- high temperatures will denature the enzyme and stop all reactions from occurring
Describe the method you would investigate the effect of pH on enzyme activity. [6 marks]
Answer (six from):
- place a beaker of water on a Bunsen burner at about 35°C
- put two drops of iodine solution into each spot of a spotting tile
- add 2cm3 of amylase enzyme solution to a test tube
- place 2cm3 of starch solution into the same tube
- add 1cm3 of pH solution to the tube
- mix the solution in the test tube and place it into the beak of water on the Bunsen burner
- use a pipette to remove a few drops of solution every 20 seconds from the test tube and put them into a different well of the spotting tile
- repeat until the iodine solution stops turning black
- record the time this takes
- repeat with different pH solutions
Describe the similarities and differences between plant and animal cells. [6 marks]
Possible content to be included (additional content must be scientifically correct and relevant):
-they are both eukaryotic so have a nucleus
- they both possess:
- cell membranes to control what enters and exits a cell
- cytoplasm where reactions occur
- ribosomes where proteins are made
- mitochondria where respiration occurs
- plant cells additionally have:
- chloroplasts where photosynthesis occurs
- a permanent vacuole filled with sap
- a cell wall made of cellulose for support
Compare and contrast diffusion and active transport. [6 marks]
- diffusion is the net movement of molecules from an area of high to lower concentration
- active transport is the net movement of molecules from an area of low to higher concentration
- diffusion is a passive process and does not require energy
- active transport is an active process and so does require energy
- diffusion occurs down a concentration gradient
- active transport occurs up a concentration gradient
- one mark for suitable example of diffusion, eg oxygen diffuses from the alveoli into the blood in the lungs
- one mark for suitable example of active transport, eg plants use active transport to absorb nitrates from the soil
Explain the lock and key model of enzyme action, including how they are denatured. [6 marks]
- the key is the enzyme and the substrate is the lock
- the key is specific for the lock like an enzyme is for its substrate
- extremes of pH or temperature denature enzymes
- this alters the shape of the active site
- so the key will no longer fit into the lock
- the substrate can no longer be broken down or joined together
Describe the process of diffusion of oxygen in the body. Explain how cells are specialised for this. [4 marks]
Answer (four from):
- oxygen diffuses from high concentrations in the alveoli to the blood
- the alveoli have a large surface area [1 mark], are moist [1 mark] and have short distances to the blood cells [1 mark] to maximise this
- red blood cells carry oxygen around the body
- they have a biconcave shape [1 mark] and no nucleus [1 mark] to maximise the oxygen they can carry
- oxygen then diffuses from high concentration in the blood to low concentration in the body cells
Describe how both the enzymes of the digestive system and its adaptations help break down foods. [5 marks]
Answer (five from):
- carbohydrase enzymes break down carbohydrates into sugars
- they are produced in the mouth, pancreas and small intestine
- lipase enzymes break down fats and oils into fatty acids and glycerol
- they are produced in the pancreas and small intestine
- protease enzymes break down proteins into amino acids
- they are produced in the stomach, pancreas and small intestine
- the small intestine is about 4 metres long [1 mark] and has millions of tiny projections [1 mark] called villi [1 mark] which increase the surface area [1 mark] to increase diffusion [1 mark]
Explain how plant roots are adapted for osmosis and active transport and give an example of a substance absorbed by each process. [4 marks]
Answer (four from):
- osmosis is the net movement of molecules from an area of high to lower concentration across a partially permeable membrane
- active transport is the net movement of molecules from an area of low to high concentration and requires energy
- plants use active transport to absorb nitrates which are in low concentrations in the soil and higher concentrations in the plant
- plants have root hair cells
- these increase the surface area of the plant in contact with the soil
- this allows greater osmosis and active transport
