biology mocks paper 1.

explain why muscle cells contain mitochondria.

muscles need large amount of energy for contraction. this energy is supplied from respiration in mitochondria. 

explain why all plant cells contain mitochondria but only some contain chloroplasts. 

mitochondria releases energy and all cells need energy, but only leaf (and stem) cells are exposed to light and so have chloroplasts for photosynthesis. 

the main function of fat cells is to store fat. xyz cells secrete pancreatic juice, which contains many different enzymes. suggest an explaination for why xyz cells contain many more ribosomes than fat cells.

enzymes are proteins and proteins are made on ribosomes. fat cell don’t produce as many proteins as xyz cells.

breathing can expose to dust, dirt and bacteria. explain how cells in the lungs are specialised to protect us from these.

epithelial cells line tubes (such as trachea). mucus traps dirt / dust / bacteria and cilia move mucus along the tubes away from lungs.

the egg cell is much larger than the sperm cell. give a reason to explain why.

the egg cell contains nutrients in the cytoplasm to supply the growing embryo. 

In filamentous algae, telophase is not followed by cytokinesis. state what the result will be.

(telophase ends when the nuclear membranes re-form. think about what normally occurs next and what might be the result if it didn,t happen.)

the nuclei divide by mitosis (1) but the two new cells do not separate from one another.

describe one way in which you could measure the growth of a plant.

measure it’s change in height over time. if the measurements increase over time, then the plant is growing.

describe what a percentile chart is used for.

a percentile chart compares the growth of an individual (1) against the growth of other individuals of the same sex and age. (1)

explain why an increase in the size of a balloon is not an example of growth but an increase in the size of a child.

the increase in size of a balloon is not a permanent increase in size, (1)  while the increase in a size of a child is a permanent increase in the number of cells in the child’s body. (1)

Q) 2a - workbook page 17

20.4

describe one other way you could measure the growth of the seedlings.

any one from:

height (1), measured with a ruler ensuring the stem is vertical (1)

measure shoots/leaves (1) by counting numbers (1)

describe how you would test for the presence of lipids (fats and oils) in a sample of food.

mix food with ethanol and shake (1). pour some mixture into water and shake again (1). cloudy emulsion will form if lipids present (1).

in the second experiment, the student followed this method:

1. soak a broad bean seed in water, then cut it in two.

2. place the cut face on a petri dish containing starch agar.

3. leave the plate for 48 hours at 20*C.

4. remove the seed, then add iodine solution to the plate. record any changes seen. The student noted that the starch agar turned blue-black everywhere, except where it had been covered by the seed. describe hoe this result explains the result of the first experiment (workbook, page 10: question 2b).

during germination enzymes digest starch (1) and produce reducing sugars (1).

explain what is meant by the active site of an enzyme.

the part of the enzyme molecule where the substrate fits; (1) where the reaction takes place.

enzymes in the human liver have an optimum temperature of about 37*C. explain why our body temperature is controlled to stay at about 37*c.

this means that enzymes are always at their optimum temperature, (1) so that the reactions occur at the fastest rate. (1)

the enzyme invertase digests sucrose to glucose and fructose. explain why invertase will not digest the sugar lactose.

the shape of the active site of invertase matches the shape of sucrose but not lactose (1), so invertase cannot combine with lactose and catalyst its digestion (1).

pepsin and trypsin are proteases. pepsin is produced in the stomach (pH2), and trypsin is found in pancreatic juice (pH 8.6) released into the small intestine. saliva and pancreatic juice both contain amylase. the graph shows the effect of pH on the activity of these enzymes.

use this information (workbook, page 7; Q3 graph) to explain why proteins are digested in the stomach and small intestine, but starch is only digested in the mouth and small intestine.

amylase digests starch in the mouth but is denatured in  the stomach (1); pepsin has a pH optimum ~2 so digests proteins in the stomach (1); pancreatic juice neutralises stomach acidity (1) ; so trypsin and amylase will work in the small intestine (1).

explain why different digestive enzymes are needed in the digestive system.

many different enzymes are needed because they are specific for different food molecules (1); digestion breaks down the food molecules into molecules small enough to be absorbed (1).

explain the importance of enzymes as biological catalysts in building the molecules needed in cell and tissues.

synthesis reactions occur too slowly
(1); enzymes are biological catalysts and speed up reactions (1).

Q. biological washing powders contain enzymes that help to break down food stains on clothes.

a) eggs are rich in protein. explain which type of enzyme is needed to remove egg stains from clothes.

b) explain why biological washing powders work better below 40*C. (think about what biological washing powders contain and what effect  temperature might have.

a) protease (1); needed to break down egg stain, which is made from protein (1).

b) the enzyme is denatured / active site destroyed (1) at higher temperatures (1), so it would not digest stains as well / would be less active (1).

define osmosis

osmosis is the net movement of water molecules from a region of higher concentration to a region of lower concentration across a partially permeable membrane.

give one similarity between diffusion and osmosis.

neither diffusion nor osmosis needs energy. 

a plant root is treated with a poison that prevents respiration. explain whether the root cells will still be able to absorb water and mineral ions from a dilute solution. 4 marks

the cell will still be able to absorb water (1) by osmosis because that is a passive process. (1) the cells will not be able to absorb mineral ions; (1) mineral ions are absorbed by active transport and that needs energy from respiration. (1)

define diffusion. (2 marks)

movement of particles (1) from high concentration to low concentration (1).

the blood in the lungs contains less oxygen and more carbon dioxide than the air. explain why oxygen moves from the air to the blood and carbon dioxide moves from the blood to the air. (3 marks)

gas particles move down the concentration gradient (1); there is high concentration of oxygen in the air, low concentration in blood (1) and low concentration of carbon dioxide in the air, high concentration in the blood (1).

when starch is digested to glucose it is important that all the glucose is absorbed from the small intestine. explain why this process requires energy. (2 marks)

glucose must be moved against a concentration gradient (1) by active transport that requires energy (1).

Mendel used the results from his experiments to devise his three laws of inheritance.

1. each gamete receives only one factor for a characteristic.

2. the version of a factor that a gamete receives is random and does not depend on the other factors in the gamete.

3. some versions of a factor are more powerful than others and always have an effect in the offspring. Mendel did not know what these ‘factors’ actually were. explain how our understanding of genes and chromosomes has confirmed his laws. (4 marks)

there are two copies of each chromosome in body cells (1); each copy has the same genes in the same order (1); a gene is a short piece of DNA at a point on a chromosome (1); genes come in different forms called alleles that produce different varitions of the characteristic (1).