B2: Cell Division

Question 1

What are 3 specialised cells in animals?

Answer 1

Sperm cells
Nerve cells
Muscle cells

Question 2

What is differentiation?

Answer 2

When a cell changes (adapts?) to carry out a specific function, so it becomes specialised.

Question 3

What is a specialised cell?

Answer 3

A cell which has adaptations which help it to carry out a particular function.

Question 4

What is the job of the sperm cell?

Answer 4

To join with an ovum (fertilisation) and combine its genetic information with the ovum

Question 5

How is a sperm cell specialised for its job?

Answer 5

Contains genetic information in the nucleus - contains half of the normal adult cell.
Long tail, allowing them to swim to the ovum.
Streamlined head to make it easier to swim.
Packed with mitochondria, providing energy for swimming.
Contain enzymes which allow them to digest their way through the outer layer of the ovum.

Question 6

What is the job of a nerve cell?

Answer 6

Send electrical impulses around the body.

Question 7

How is a nerve cell specialised for its job?

Answer 7

Long axon - carries the impulse from one part of the body to another.
Axon covered with myelin - insulates the axon and speeds up the transmission of nerve impulses.
Synapses at the end of axon - junctions which allow the impulse to pass from one nerve cell to the other.
Dendrites - increase surface area, so that other nerve cells can connect more easily.

Question 8

What is the job of a muscle cell?

Answer 8

Contraction

Question 9

How is a muscle cell specialised for its job?

Answer 9

Contain protein fibres which can change their length - when the cell contracts, they shorten and decrease the length of the cell.
Packed with mitochondria - provide energy for muscle contraction.
Work together to form muscle tissue.

Question 10

What are some examples of specialised plant cells?

Answer 10

Xylem cells
Phloem cells
Root hair cells

Question 11

What is the job of a root hair cell?

Answer 11

Increase the surface area of the root - so it can absorb water and dissolved minerals more efficiently.

Question 12

How is a root hair cell specialised for its job?

Answer 12

Hair - increases SA of the root.
No chloroplasts - as they are underground and do not photosynthesise due to the absence of light.

Question 13

What is the job of a xylem cell?

Answer 13

Found in plant stem.
Long tubes which carry water and dissolved minerals from the roots to the leaves

Question 14

How are xylem cells specialised for their job?

Answer 14

Form long tubes.
Thick wall containing lignin - provides support to the plant.
Because cell walls are sealed with lignin, it causes the xylem cells to die.
End walls between cells have broken down - cells now form a long tube so water and dissolved minerals can flow easily.
No nucleus, cytoplasm, vacuole or chloroplasts (no internal structures), makes it easier for water and minerals to flow.

Question 15

What is the job of phloem cells?

Answer 15

Carry dissolved sugars up and down the plant.

Question 16

How is a phloem cells specialised for its job.

Answer 16

Consists of 2 different types of cells:
Phloem vessel cells - contain no nucleus and only limited cytoplasm. End walls have pores (sieve plates). Both features allow dissolved sugars to move through the cell interior.
Each phloem vessel cell has a companion cell connected by pores. Mitochondria in a companion cell provides energy to the phloem vessel cell.

Question 17

How do bacteria multiply?

Answer 17

Through simple cell division - one bacterial cell splits into two bacterial cells (binary fission).

Question 18

How often do bacteria multiply?

Answer 18

Once every 20 mins, as long as they have enough nutrients and the temperature is suitable.

Question 19

How do you calculate the number of bacteria after a certain period of time?

Answer 19

Number of bacteria = 2^n
where n = number of rounds of division.

Question 20

What is the cell cycle?

Answer 20

The process through which a cell divides.

Question 21

What is the first stage of the cell cycle?

Answer 21

DNA replicates to form 2 copies of each chromosome.
Cell grows and copies its internal structures, such as mitochondria and ribosomes.

Question 22

What is the second stage of the cell cycle?

Answer 22

Mitosis takes place -
one set of chromosomes is pulled to each end of the cell. Nucleus divides.

Question 23

What is the final stage of the cell cycle?

Answer 23

Cytoplasm and cell membrane divide to form identical cells.

Question 24

What are the functions of mitosis?

Answer 24

Essential for growth and development of multicellular organisms (like plants and animals).
Mitosis takes place when an organism repairs itself e.g. when a broken bone heals.
Happens during asexual reproduction.

Question 25

What is a stem cell?

Answer 25

An unspecialised cell which can give rise to more cells of the same type and can differentiate to form other types of cells.

Question 26

What is an embryonic stem cell?

Answer 26

When a sperm cell joins with an egg cell, the fertilised ovum undergoes mitosis and forms an embryo (group of cells). These cells continue to undergo mitosis and change to form specialised cells.
Cells in an early embryo have not differentiated - any cell is capable of differentiating into any type of body cell.

Question 27

What are some sources of stem cells?

Answer 27

Human embryos
Bone marrow

Question 28

What can stem cells in the bone marrow differentiate into?

Answer 28

Bone marrow stem cells differentiate to form cells found in our blood e.g. red blood cell, white blood cell and platelets.

Question 29

How are adult stem cells different to embryonic stem cells?

Answer 29

They can only differentiate to form certain types of cells.

Question 30

Describe how leukaemia can be treated using bone marrow transplants

Answer 30

The patient’s existing bone marrow is destroyed using radiation.
Patient then receives transplant of bone marrow from donor. Stem cells in the bone marrow now divide and form new bone marrow. Also differentiate and form blood cells.

Question 31

What are the problems with bone marrow transplants?

Answer 31

Bone marrow has to be compatible with the patient, otherwise, white blood cells produced by the donated bone marrow could attack the patient’s body.
Risk that viruses can be passed from donor to patient.

Question 32

What are some uses of stem cells?

Answer 32

Bone marrow transplants
Therapeutic cloning

Question 33

What happens in therapeutic cloning?

Answer 33

An embryo is produced with the same genes as the patient. This means that stem cells from the embryo can be transplanted into the patient without being rejected by the patient’s immune system. Once inside the patient, the stem cells begin to differentiate to replace cells which have stopped working correctly.

Question 34

What is therapeutic cloning useful for?

Answer 34

Treating diabetes or paralysis.

Question 35

What are the ethical or religious objections to therapeutic cloning?

Question 36

What are the stem cells in plants like?

Answer 36

Roots and buds contain meristem tissue (stem cells that can differentiate into any type of tissue).

Question 37

What are meristem tissue useful for?

Answer 37

To clone a rare plant and prevent it from going extinct, or we can produce cloned crop plants for farmers.