National 4 Biology
Unit 1 Cell Biology
Homework Questions
Key Area 1 – Cell division and its role in growth and repair
1. Diagrams A, B and C represent stages of cell division.
Add the letters A, B and C to the empty cells below to show the correct order
in which they occur.
2. What is the condition called when cells divide without stopping?
______________
Key Area 2 – DNA, genes and chromosomes
1. Read the following passage and use the information to answer the questions.
Twins
Multiple births have been on the rise with increasing numbers of twins being
born. There are several reasons for this, including the growing use of fertility
drugs and the fact that more, older women are having babies. Between 1996 and
2006 there was a 182% increase in multiple births in women aged 35 and over.
About 1·25% of births from natural conception results in twins, but this
increases to 25% if fertility drugs are used.
Twins can be identical or non-identical. An ultrasound scan can help to determine
which is the case. If the babies develop together in a single sac with no
separating membrane, or share one placenta, they are likely to be identical.
Identical twins will always be the same sex because they carry the same genetic
information. However, the only sure way to tell if twins are identical is to have a
DNA test.
The chance of having identical twins is about 1 in 250 births. The chance of
having non-identical twins varies according to whether there is a history of nonidentical twins in the mother's family. If there is, she is more likely to have
them. About 33% of all twins born are identical. They are formed when one egg
is fertilised by one sperm and then the zygote divides into two halves which
develop separately. Non-identical twins form when two eggs are fertilised by
two different sperm.
(a) Give two reasons for the increase in the number of twins being born.
1 __________________________________________________________
2 __________________________________________________________
(b) Give two pieces of evidence from an ultrasound scan that would suggest that
twins are identical.
1 __________________________________________________________
2 __________________________________________________________
(c) What is the only sure way to tell whether or not twins are identical?
___________________________________________________________
(d) How do identical twins form?
___________________________________________________________
(e) What percentage of all twins are non-identical?
______________
(f) Which parent's family history has more influence on the chance of having
non-identical twins?
______________
2. Decide if each statement about DNA is TRUE or FALSE then tick ( ) the
correct box.
If the statement is FALSE, write the correct word(s) in the Correction box to
replace the word(s) underlined in the statement.
Statement
Genes are found on the DNA.
True
False
Correction
Chromosomes are found in the
nucleus.
Each gene codes for a
carbohydrate.
Key Area 3 & 8 – Therapeutic use of cells & Controversial biological
procedures
1. Which of the following conditions does not or could not use stem cells to help
treat it?
A
B
C
D
Cancer
Replacement Organs
HIV
Parkinson’s Disease
2. Why is embryonic stem cell research controversial?
___________________________________________________________
___________________________________________________________
Key Area 4 – Properties of enzymes and use in industries
1. (a) The following graph shows the relationship between pH and the rate of
activity of two different enzymes.
(i) Identify the enzyme which is likely to be pepsin and give a reason for your
answer.
Enzyme______________
Reason _____________________________________________________
___________________________________________________________
(ii) Use information from the graph to answer the following questions.
1 Between which pH values are both enzymes active?
Between ______________ and ______________
2 How many times greater is the rate of activity of enzyme B at pH 7 than at
pH 8?
Space for calculation
______________
2. Highlight the correct term.
Enzymes (speed up/slow down) a chemical reaction.
Enzymes are (changed/unchanged) by a chemical reaction.
Enzymes are (specific/unspecific).
Key Area 5 – Properties of microorganisms and use in industries
1. Name the micro-organism which is added to pasteurised milk to produce
yoghurt.
___________________________________________________________
2. The table below shows the percentage of ingredients in a washing powder.
Ingredient
Percentage
(%)
bleach
15
builder
optical
1
brightener
soap
5
surfactant
30
(a) Complete the table by calculating the percentage of builder in the
detergent.
Space for calculation
______________
(b) Use the information in the table to label the pie chart correctly.
3. (a) The diagram below shows some steps in cheese making.
(i) Name substance X.
___________________________________________________________
(ii) Describe what rennet does to the milk to produce substance X.
___________________________________________________________
___________________________________________________________
Key Area 6 – Photosynthesis — limiting factors
1. (a) Photosynthesis is the process by which plants make food. Complete the
word equation for photosynthesis.
water + _________________  glucose + ___________________
(b) Name the substance, found in a plant cell, which converts light energy to
chemical energy.
_____________________________________
2. The following graph shows the effect of increasing carbon dioxide
concentration on the rate of photosynthesis at two different temperatures. All
other factors were kept constant.
From the evidence in the graph, what are the limiting factors at points X and Y?
X _________________
Y _________________
Key Area 7 – Factors affecting respiration
1. The diagram shows a method used to investigate the energy content of a
variety of foods.
The rise in temperature can be used to calculate the energy content of each
food in kilojoules.
The results are shown in the table.
Type of food
mass (g)
cheese
fish
steak
carrot
apple
1.0
1.0
1.0
1.0
1.0
energy content
(kilojoules)
17.0
0.5
13.9
1.8
2.5
(a) State two factors, not already mentioned, that should be kept constant for
a valid comparison to be made between the foods.
1 __________________________________________________________
2 __________________________________________________________
(b) Suggest why the energy contents found in the investigation might not have
been as high as expected.
___________________________________________________________
___________________________________________________________
2. Respiration is controlled by enzymes, what factor could affect the rate of
respiration?
_________________