Exam questions · Biology
Cell Division
- 33 exam questions
- 89 marks
- 32 quick checks
Chromosomes, Genes and DNA
Just this lesson-
1 Name [1 mark]
Name the part of a cell that contains the chromosomes.
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Model answer
The nucleus.
Mark scheme
- Nucleus — 1 mark
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2 State [1 mark]
State the number of chromosomes in a human body cell.
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Model answer
46 (or 23 pairs).
Mark scheme
- 46 / 23 pairs — 1 mark
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3 Name [3 marks]
Figure 1 shows how genetic material is stored in a cell. Name the structures labelled A, B and C.
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Model answer
A is the nucleus. B is a chromosome. C is a gene.
Mark scheme
- A: nucleus — 1 mark
- B: chromosome — 1 mark
- C: gene — 1 mark
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4 Describe [2 marks]
Describe the relationship between a gene and a chromosome.
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Model answer
A chromosome carries a large number of genes. A gene is a short section of the DNA that makes up a chromosome.
Mark scheme
- A chromosome carries many genes — 1 mark
- A gene is a section of the DNA of a chromosome — 1 mark
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5 Calculate [2 marks]
A fruit fly body cell has 8 chromosomes. Calculate the number of pairs of chromosomes in the cell.
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Model answer
8 ÷ 2 = 4 pairs.
Mark scheme
- Divides the number of chromosomes by 2 — 1 mark
- 4 pairs — 1 mark
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6 Describe [3 marks]
Describe how the chromosomes are arranged in a human body cell, and where they came from.
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Model answer
They are in pairs, 23 pairs in all (46 chromosomes). One chromosome in each pair came from the mother and the other from the father.
Mark scheme
- Chromosomes are in pairs — 1 mark
- 23 pairs / 46 chromosomes — 1 mark
- One of each pair from each parent — 1 mark
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7 Describe [4 marks]
Describe where DNA is found in a cell and how it is organised.
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Model answer
DNA is found in the nucleus of the cell. It is organised into chromosomes, each of which is one long, coiled DNA molecule. Each chromosome carries many genes, and a gene is a short section of DNA. In body cells the chromosomes are in pairs.
Mark scheme
- DNA is in the nucleus — 1 mark
- Organised into chromosomes — 1 mark
- Each chromosome carries many genes — 1 mark
- A gene is a section of DNA / chromosomes in pairs — 1 mark
Quick check
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1
Where are chromosomes found in a human body cell?
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B: In the nucleus
Chromosomes are in the nucleus. The cytoplasm, cell membrane and mitochondria do not contain them.
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2
What is a chromosome made of?
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C: DNA
A chromosome is a long, coiled molecule of DNA.
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3
Which of these is the smallest?
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D: A gene
A gene is a short section of DNA, which makes up part of a chromosome. A chromosome is inside the nucleus, and the nucleus is inside the cell.
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4
How many pairs of chromosomes are there in a human body cell?
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A: 23
A human body cell has 46 chromosomes, which is 23 pairs.
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5
A body cell has 18 chromosomes. How many pairs is that?
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C: 9
A pair is two chromosomes, so 18 ÷ 2 = 9 pairs.
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6
Where does each chromosome in a pair come from?
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B: One from each parent
One chromosome of each pair comes from the mother and the other comes from the father.
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7
Which statement about genes is correct?
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D: A gene is a short section of DNA
A gene is a short section of DNA. A chromosome is a long DNA molecule that carries many genes.
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8
A dog body cell has 78 chromosomes and a human body cell has 46. What does this tell you?
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A: Chromosome number is different in different species and says nothing about complexity
Different species have different numbers of chromosomes, and a larger number does not make an organism more complex. It is what the genes say that matters.
The Cell Cycle and Mitosis
Just this lesson-
1 Name [1 mark]
Name the type of cell division that produces two genetically identical cells for growth and repair.
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Model answer
Mitosis.
Mark scheme
- Mitosis — 1 mark
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2 State [2 marks]
State two reasons why mitosis is important in a human.
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Model answer
Any two from: growth (and development); repair of damaged tissue; replacement of worn-out cells.
Mark scheme
- Growth / development — 1 mark
- Repair of damaged tissue — 1 mark
- Replacement of cells — 1 mark
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3 Name [3 marks]
Figure 1 shows the three stages of the cell cycle. Name the stages A, B and C.
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Model answer
A is growth and DNA replication (accept interphase). B is mitosis. C is the division of the cytoplasm and cell membrane (accept cytokinesis).
Mark scheme
- A: growth and DNA replication — 1 mark
- B: mitosis — 1 mark
- C: the cytoplasm (and cell membrane) divides — 1 mark
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4 Describe [3 marks]
Describe what happens in a cell during the first stage of the cell cycle, before mitosis.
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Model answer
The cell grows. The number of sub-cellular structures, such as ribosomes and mitochondria, increases. The DNA replicates to form two copies of each chromosome.
Mark scheme
- The cell grows — 1 mark
- More ribosomes and mitochondria / sub-cellular structures — 1 mark
- DNA replicates, giving two copies of each chromosome — 1 mark
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5 Explain [2 marks]
A human skin cell has 46 chromosomes. It divides by mitosis. State the number of chromosomes in each new cell, and explain your answer.
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Model answer
46 in each new cell. The DNA is copied before the cell divides, and one copy of each chromosome is pulled to each end, so each new cell gets a full set.
Mark scheme
- 46 — 1 mark
- DNA replicated first / one copy of every chromosome goes to each new cell — 1 mark
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6 Put in order [2 marks]
Figure 2 shows six stages of mitosis in the wrong order. Write the letters in the correct order, starting with the cell before it divides.
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Model answer
B, E, D, A, F, C.
Mark scheme
- B first and C last — 1 mark
- E, D, A, F in the correct order between them — 1 mark
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7 Calculate [2 marks]
A cell divides by mitosis. Every new cell then divides, and this happens 5 times in total. Calculate the number of cells at the end.
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Model answer
\(2^{5} = 32\) cells.
Mark scheme
- Doubles each time / \(2^{5}\) — 1 mark
- 32 — 1 mark
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8 Explain [4 marks]
Explain how mitosis helps a cut in the skin to heal.
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Model answer
Cells at the edge of the cut divide by mitosis. This makes new cells, which fill the gap and replace the damaged cells. The new cells are genetically identical to the original skin cells, so they have the same genes and do the same job, and the skin is repaired.
Mark scheme
- Cells next to the cut divide by mitosis — 1 mark
- New cells are made — 1 mark
- They fill the gap / replace damaged cells — 1 mark
- New cells are genetically identical, so they do the same job — 1 mark
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9 Describe and explain [6 marks]
Describe the stages of the cell cycle, and explain why mitosis produces two genetically identical cells.
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Model answer
In the first stage the cell grows and the numbers of ribosomes and mitochondria increase. The DNA replicates, giving two identical copies of each chromosome. In mitosis, one set of chromosomes is pulled to each end of the cell and the nucleus divides. Finally the cytoplasm and cell membrane divide, forming two cells. The two cells are genetically identical because the DNA was copied exactly before division and each new cell receives one copy of every chromosome, so each has the same genes and the same number of chromosomes.
Mark scheme
- The cell grows and makes more ribosomes and mitochondria — 1 mark
- DNA replicates / two copies of each chromosome — 1 mark
- In mitosis one set of chromosomes is pulled to each end — 1 mark
- Nucleus divides, then cytoplasm and membrane divide — 1 mark
- Each new cell gets one copy of every chromosome — 1 mark
- So cells have the same genes / are genetically identical — 1 mark
Quick check
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1
How many cells does one cell make when it divides by mitosis?
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B: Two
Mitosis, followed by division of the cytoplasm, makes two cells.
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2
What happens to the DNA before mitosis?
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C: It is copied
The DNA replicates, giving two identical copies of each chromosome, so that each new cell can have a full set.
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3
What happens to the chromosomes in mitosis?
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A: One set is pulled to each end of the cell
One set of chromosomes is pulled to each end of the cell and the nucleus divides.
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4
A human cell with 46 chromosomes divides by mitosis. How many chromosomes are in each new cell?
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D: 46
Mitosis makes genetically identical cells with the same number of chromosomes as the parent cell.
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5
Which of these is NOT a job of mitosis?
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C: Making egg cells with half the chromosomes
Mitosis is used for growth, repair and replacement. Making egg and sperm cells uses a different type of cell division, which you meet later in the course.
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6
A cell divides by mitosis 3 times. Every new cell also divides. How many cells are there at the end?
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B: 8
The number doubles each time: 1, 2, 4, 8. That is 2 to the power 3, which is 8.
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7
What are the two new cells formed by mitosis called?
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A: Daughter cells
The two cells formed when a cell divides are called daughter cells.
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8
A student says: "The two new cells are identical to the parent cell because they are the same size." What is wrong with this?
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D: Identical means the same genes, and it is the DNA copying that makes this so
Cells being genetically identical means they have the same genes. It is the copying of the DNA before division that makes them identical, not their size or shape.
Stem Cells
Just this lesson-
1 Name [1 mark]
Name the plant tissue that contains stem cells.
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Model answer
Meristem.
Mark scheme
- Meristem — 1 mark
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2 Describe [2 marks]
Describe what is meant by a stem cell.
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Model answer
An undifferentiated cell that can divide to make more cells, and that can differentiate into specialised cells.
Mark scheme
- An undifferentiated cell — 1 mark
- Can divide / produce more cells and differentiate into other cell types — 1 mark
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3 Name [3 marks]
Figure 1 shows three places where stem cells are found. Name the places A, B and C.
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Model answer
A is an embryo. B is (adult) bone marrow. C is a meristem (in a plant).
Mark scheme
- A: embryo — 1 mark
- B: bone marrow — 1 mark
- C: meristem / plant shoot tip — 1 mark
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4 State [2 marks]
State two places in the human body where stem cells are found.
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Model answer
In the embryo and in the (adult) bone marrow.
Mark scheme
- Embryo — 1 mark
- (Adult) bone marrow — 1 mark
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5 Describe [2 marks]
Describe one difference between stem cells from human embryos and stem cells from adult bone marrow.
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Model answer
Embryonic stem cells can become most types of human cell, but adult bone marrow stem cells can become fewer types, such as blood cells.
Mark scheme
- Embryonic stem cells can form most types of cell — 1 mark
- Bone marrow stem cells can form fewer types / mainly blood cells — 1 mark
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6 Explain [3 marks]
Figure 2 shows a young plant. Name the tissue found at A and at B, and explain why the plant can keep growing throughout its life.
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Model answer
A and B are both meristem tissue (meristems). The plant can keep growing because meristems contain stem cells that keep dividing and differentiating throughout the life of the plant.
Mark scheme
- A and B are meristems — 1 mark
- Stem cells in meristems keep dividing — 1 mark
- And differentiate into any type of plant cell, throughout its life — 1 mark
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7 Explain [3 marks]
Explain how stem cells help a human embryo to develop into a baby.
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Model answer
Stem cells in the embryo divide to make many more cells. The cells then differentiate into the different types of specialised cell, such as nerve, muscle and blood cells. The specialised cells form the tissues and organs of the baby.
Mark scheme
- Stem cells divide to make more cells — 1 mark
- Cells differentiate into different specialised cells — 1 mark
- Specialised cells form the tissues and organs — 1 mark
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8 Explain [3 marks]
Stem cells from bone marrow can be used to replace blood cells but not brain cells. Explain why.
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Model answer
Adult bone marrow stem cells can only differentiate into a limited range of cell types. They can form blood cells, but they cannot differentiate into most other types of cell, such as brain cells.
Mark scheme
- Adult stem cells differentiate into fewer types of cell — 1 mark
- They can form blood cells — 1 mark
- They cannot form most other types, such as brain cells — 1 mark
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9 Compare [6 marks]
Compare stem cells in human embryos, in adult bone marrow and in plant meristems.
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Model answer
All three are stem cells, which means they are undifferentiated, they can divide, and they can differentiate. Embryonic stem cells are found in human embryos and can become most types of human cell. Stem cells in adult bone marrow can become fewer types of cell, including blood cells. In plants, meristem tissue is found at the tips of shoots and roots and can become any type of plant cell, throughout the life of the plant. So the difference is in the range of cells each can make and the length of time they are active.
Mark scheme
- All are undifferentiated cells that divide and can differentiate — 1 mark
- Embryos: most types of human cell — 1 mark
- Bone marrow: fewer types, such as blood cells — 1 mark
- Meristems: any type of plant cell — 1 mark
- Meristems are in the tips of shoots and roots — 1 mark
- Meristems stay active throughout the plant's life / embryonic cells more types than adult — 1 mark
Quick check
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1
What does undifferentiated mean?
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C: Not specialised for a particular job
An undifferentiated cell has not yet specialised for a particular job.
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2
Which cells can differentiate into most types of human cell?
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B: Embryonic stem cells
Stem cells from human embryos can be made to differentiate into most types of human cell.
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3
What can stem cells from adult bone marrow form?
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A: Many types of cell, including blood cells
Adult bone marrow stem cells can form many types of cell, including blood cells.
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4
Where are meristems found?
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D: At the tips of the shoots and roots
Meristems are found at the tips of shoots and roots, where the plant grows.
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5
What can meristem cells become?
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C: Any type of plant cell
Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant.
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6
Why can a plant keep growing throughout its life?
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B: Meristems keep producing new cells
Its meristems contain stem cells that keep dividing and differentiating for the whole life of the plant.
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7
Why is a red blood cell NOT a stem cell?
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A: It is specialised and cannot become other types of cell
A red blood cell is specialised for carrying oxygen. It has differentiated and does not divide to make other cell types.
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8
Which statement about stem cells is correct?
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D: Embryonic stem cells can become more types of cell than adult stem cells
A stem cell can make more cells like itself and some of the cells it makes can differentiate. Embryonic stem cells can become more types of cell than adult stem cells.
Using Stem Cells
Just this lesson-
1 Name [1 mark]
Name one medical condition that stem cells may be able to help treat.
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Model answer
Diabetes, or paralysis (accept other suitable conditions).
Mark scheme
- Diabetes / paralysis — 1 mark
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2 Explain [2 marks]
In therapeutic cloning, the stem cells are not rejected by the patient's body. Explain why.
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Model answer
The embryo is made with the same genes as the patient, so the cells made from it are not recognised as foreign by the patient's body.
Mark scheme
- The embryo has the same genes as the patient — 1 mark
- So the body does not see the cells as foreign / does not reject them — 1 mark
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3 Describe [3 marks]
Figure 1 shows the stages of therapeutic cloning. Describe what happens in stages 2, 3 and 4.
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Model answer
In stage 2 an embryo is produced that has the same genes as the patient. In stage 3 stem cells are taken from the embryo. In stage 4 the stem cells are made to differentiate into the type of cell that is needed.
Mark scheme
- Stage 2: an embryo with the same genes as the patient — 1 mark
- Stage 3: stem cells taken from the embryo — 1 mark
- Stage 4: stem cells differentiate into the cells needed — 1 mark
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4 State [2 marks]
State two risks or objections to the use of stem cells in medicine.
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Model answer
Any two from: a risk of transferring a viral infection; ethical objections, such as destroying an embryo; religious objections.
Mark scheme
- Risk of viral infection — 1 mark
- Ethical objections (an embryo is destroyed) — 1 mark
- Religious objections — 1 mark
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5 Describe [3 marks]
Describe how stem cells from a plant's meristem can be used to produce clones of the plant.
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Model answer
A small piece of meristem tissue is taken from the parent plant. The stem cells in it divide and differentiate to grow into new plants. The new plants have the same genes as the parent, so they are all clones.
Mark scheme
- Meristem tissue is taken from the parent plant — 1 mark
- Cells divide and differentiate to grow into new plants — 1 mark
- New plants have the same genes as the parent (clones) — 1 mark
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6 Give [2 marks]
Give two reasons why it is useful to clone plants from stem cells.
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Model answer
Any two from: rare species can be cloned to protect them from extinction; crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers; it is quick and economical.
Mark scheme
- To protect rare species from extinction — 1 mark
- To produce many identical crop plants with a useful feature (such as disease resistance) — 1 mark
- It is quick and economical — 1 mark
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7 Explain [4 marks]
A farmer grows a crop of plants that were all cloned from one parent plant. Give one advantage and one disadvantage of growing a crop made of clones, and explain each.
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Model answer
Advantage: all the plants have the same useful features, for example disease resistance, so the crop is reliable and uniform. Disadvantage: all the plants have the same genes, so one new disease could harm every plant in the crop.
Mark scheme
- Advantage: all have the same useful feature — 1 mark
- Explained: for example disease resistance in every plant, so a uniform crop — 1 mark
- Disadvantage: all have the same genes, so no variety — 1 mark
- Explained: a new disease could harm the whole crop — 1 mark
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8 Evaluate [6 marks]
Evaluate the use of stem cells in medicine.
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Model answer
Stem cells may be able to help conditions such as diabetes and paralysis by replacing the cells that have been lost, and with therapeutic cloning the cells are not rejected because they have the same genes as the patient. This could help many people who cannot be treated now. However, the use of stem cells has risks, such as the transfer of a viral infection, and the treatments are still being developed. Some people have ethical or religious objections to using embryonic stem cells, because the embryo is destroyed, although others think this is outweighed by the benefit to patients. Adult stem cells avoid this objection but can become fewer types of cell. On balance, the potential benefits are large, but the risks have to be controlled, and the decision depends on the views of society.
Mark scheme
- Benefit: could treat conditions such as diabetes and paralysis — 1 mark
- Therapeutic cloning gives cells that are not rejected — 1 mark
- Risk: transfer of viral infection — 1 mark
- Ethical or religious objection: an embryo is destroyed — 1 mark
- Counter-argument or adult stem cells as an alternative — 1 mark
- A reasoned conclusion (weighing the benefits against the risks) — 1 mark
Quick check
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1
Which condition may stem cells help to treat?
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C: Diabetes
Treatment with stem cells may be able to help conditions such as diabetes and paralysis.
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2
In therapeutic cloning, how is the embryo made?
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B: With the same genes as the patient
The embryo is produced with the same genes as the patient.
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3
Why are the stem cells made by therapeutic cloning not rejected?
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A: They have the same genes as the patient
They have the same genes as the patient, so the patient's body does not see them as foreign.
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4
Which of these is a risk of using stem cells in medicine?
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D: Transfer of a viral infection
A viral infection could be transferred to the patient with the stem cells.
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5
Why do some people object to using embryonic stem cells?
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B: It involves destroying an embryo
Some people have ethical or religious objections, because taking stem cells from an embryo destroys the embryo.
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6
Stem cells from meristems can be used to produce what?
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C: Clones of plants
Meristem stem cells can be used to produce clones of plants quickly and economically.
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7
Which is a use of cloning plants from meristem tissue?
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A: Protecting a rare species from extinction
Rare species can be cloned to protect them from extinction, and crop plants with special features can be cloned in large numbers.
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8
A farmer clones one disease-resistant plant to make a whole field of identical plants. What is a possible drawback?
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D: A new disease could affect them all
The plants have the same genes, so a new disease that they cannot resist could damage every plant in the field.