SB2 - Cells And Control

Question 1

SB2a
1) What does diploid mean?
2) What does haploid mean?
3) What are the stages of mitosis, in order?

Answer 1

1) Diploid means a cell that contain two copies of each chromosome (two sets).
2) Haploid means that a cell contains one copy of each chromosome (one set).
3) Prophase, Metaphase, Anaphase, Telophase, Cytokinesis

Question 2

SB2a
1) What happens in interphase?
2) What happens in prophase?
3) What happens in metaphase?

Answer 2

1) In interphase, the cell makes extra sub-cellular parts (eg. mitochondria), and DNA replication (copying) occurs to make copies of all the chromosomes.
2) In prophase, the chromosomes condense, the nucleus starts to break down, and spindle fibres appear.
3) In metaphase, the chromosomes line up across the middle of the cell, and are attached to the spindle fibres.

Question 3

SB2a
1) What happens in anaphase?
2) What happens in telophase?
3) What happens in cytokinesis?

Answer 3

1) In anaphase, the spindle fibres pull chromosomes apart, and they are moved to opposite ends of the cell.
2) In telophase, a nuclear membrane forms around each set of chromosomes to form nuclei.
3) In cytokinesis, a cell surface membrane forms to separate the two cells during cytokinesis. Cells walls form in plant cells.

Question 4

SB2a
1) When are new cells produced?
2) What is the cell cycle?

Answer 4

1) New cells are produced when an organism grows, or an organism repairing itself requires new cells.
2) The cell cycle is the events that take place in a cell that produces two daughter cells, that are identical to the parent cell. This is through the growth and division of cells.

Question 5

SB2a
1) Why is mitosis important for asexual reproduction?
2) What is the difference between sexual and asexual reproduction (in terms of advantages)?

Answer 5

1) All the cells in an organism produced by asexual reproduction must be genetically identical to the parent cell.
2) Asexual reproduction is much faster than sexual reproduction because organisms do not need others for fertilisation. However, sexual reproduction produces variation, while asexual reproduction does not.

Question 6

SB2a
1) What is a tumour?
2) Describe how cancer develops
3) What are the treatment for tumours?

Answer 6

1) A tumour is a large lump of cells caused by a change in the genes that control cell division and causes the cell to divide uncontrollably by mitosis.
2) Cancer is the uncontrolled division of cells by mitosis, resulting in a tumour.
3) Tumours can be cut out or killed by radiotherapy (high-energy X-ray beams) and chemotherapy (injecting drugs that kill actively dividing cells). All these methods can damage the body and brain, and chemotherapy may not work due to the blood-brain barrier - a natural filter that only allows certain substances to get from the blood to the brain.

Question 7

SC2b
1) What is the definition of differentiation?
2) How are sperm cells adapted to their function?
3) How are egg cells adapted to their functions?
4) How are ciliated epithelial cells adapted to their function?

Answer 7

1) Differentiation is the process that changes less specialised cells into more specialised ones.
2) Sperm cells are adapted by: having an acrosome to break into the jelly coat of the egg cell, a haploid nucleus, a tail to swim, and lots of mitochondria to power the tail.
3) Egg cells are adapted by: the cytoplasm having lots of nutrients for the fertilised egg, a haploid nucleus, a jelly coat to protect the egg cell (which hardens to stop more than one sperm entering), and a cell membrane which fuses with the sperm’s cell membrane.
4) Ciliated epithelial cells are adapted by: having cilia, which sweeps substances along (such as mucus).

Question 8

SC2b
1) What is a nerve cell’s function and its adaptation?
2) What is a muscle cell’s function and its adaptation?
3) What is a fat cell’s function and adaptation?
4) What is a red blood cell’s function and adaptation?

Answer 8

1) A nerve cell’s function is to carry electrical impulses up and down the body. They are adapted by being long to cover more distance.
2) A muscle cell’s function is to contract quickly to allow movement. They are specialised by: being long, so that they have space to contract, and they have lots of mitochondria, so that they have enough energy to contract.
3) The function of a fat cell is to store lipids (fats) for the body. They are specialised by the cytoplasm of the cell being filled with large fat droplets.
4) The function of a red blood cell is to transport oxygen around the body. They are adapted by: having no nucleus, so there is more room to store oxygen, it has a large surface area for diffusion, and it contains haemoglobin to carry oxygen.

Question 9

SB2b
1) What is growth?
2) What is a percentile growth chart?
3) How do percentile charts work?
4) What would be an indication of a health problem?

Answer 9

1) Growth in animals is an increase in cell number and size.
2) A percentile growth chart is a chart used to compare a baby to the growth of other babies.
3) The lines tell you what proportion of the population has a value higher of lower than the baby. If a baby is born on the 50th percentile for height, then in every hundred babies, 50 will be taller and 50 will be shorter. If a baby is born on the 10th percentile for mass, then in every hundred babies, 90 will be heavier and 10 will be lighter.
4) Health visitors and parents tend to worry more when babies change their position on these charts over time. They would probably be more concerned about a baby that drops from the 50th to the 10th percentile than one that remains on the 10th percentile. This change could be an indication of a health problem.

Question 10

SB2c
1) What are meristems?
2) What are the 3 stages of growth in meristems?
3) How can growth in plants be calculated?
4) Explain why cell differentiation is important in the development of specialised cells in plants

Answer 10

1) Meristems are undifferentiated cells in a plant that divide by mitosis in order to produce more cells.
2) Mitosis, elongation and differentiation. The cells in meristems divide by mitosis. The plant gets longer through elongation, and then they differentiate into more specialised cells.
3) Growth in plants (percentage change) can be calculated using this formula: ((final value - starting value) / starting value) x 100%
4) Cell differentiation is important because it allows cells to specialize and perform specific functions in an organism. This allows for the formation of tissues and organs, and is necessary for the proper functioning of the body.

Question 11

SB2c
1) What is the function of a root hair cell and how are they specialised?
2) What is the function of a palisade cell and how are they specialised?
3) What is the function of a xylem cell and how are they specialised?

Answer 11

1) A root hair cell’s function is to absorb water and minerals. It has a large surface area to absorb water quickly, thin walls to allow water to pass through easily, and does not contain chloroplasts.
2) A palisade cell’s function is to absorb light energy for photosynthesis. Palisade cells are adapted by being column-shaped and packed with many chloroplasts. They are arranged closely together so that a lot of light energy can be absorbed.
3) The xylem is a tissue which transports water and minerals from the roots up the plant stem and into the leaves. The xylem cells are adapted by losing their end walls so the xylem forms a continuous, hollow tube. Also, they become strengthened by a substance called lignin. Lignin gives strength and support to the plant, and lignified cells are called wood.

Question 12

SB2d
1) What are stem cells?
2) What are the early stage embryo cells in humans and what do they do?

Answer 12

1) Stem cells are cells that can divide repeatedly over a long period of time to produce cells that differentiate into other types of cells. In plants, these cells are found in meristems (and are sometimes called meristem cells).
2) The cells of an early-stage embryo are embryonic stem cells that can produced any type of specialised cells. They start to develop into different areas that become the different organs.

Question 13

SB2d
1) Explain stem cells use in medicine.
2) What are ethical problems for using embryonic stem cells in medicine?

Answer 13

1) Stem cells offer a way of treating many different diseases caused by damaged cells. However, there are issues such as the fact that if the cells continue to divide after replacing the stem cells, they can cause cancer and create a tumour. They can also be rejected, meaning that the stem cells of one person are often killed by the immune system of other people they are put into.
2) There is no guarantee that the treatment will work, diseases from the stem cells could be transferred to the patient, and some people believe that it is wrong to destroy a potential human life.

Question 14

SB2e
1) What does the cerebral cortex do?
2) What does the cerebellum do?
3) What does the medulla oblongata do?
4) What does the spinal chord do?

Answer 14

1) The cerebral cortex is split into two hemispheres and makes up the majority of the brain. This controls most of our senses, language, memory, behaviour and consciousness (our inner thoughts and feelings).
2) The cerebellum is at the base of the brain, is split into two hemispheres and controls balance, co-ordination of movement and muscular activity.
3) The medulla oblongata controls unconscious activities such as your heart rate and your breathing rate. It is also responsible for reflexes such as vomiting, sneezing and swallowing.
4) The neurons that make up the medulla oblongata connect the brain to the spinal chord. The nerves in the spinal chord carry information between the brain and the rest of the body.

Question 15

SB2f
1) What are the parts of the brain, and where are they located?
2) What is a CT scan?
3) What is a PET scan?

Answer 15

1) The cerebral cortex (the main large section of the brain), the cerebellum (underneath the cerebral cortex), and the medulla oblongata (next to the spinal chord).
2) A CT scan shows the shapes of the structures of the brain. An x-ray beam moves in a circle around the head and detectors measure the absorption of the X-rays. A computer uses this information to build up a view of inside the body as a series of slices.
3) A PET scan shows brain activity. The patient is injected with radioactive glucose. More active cells take in more glucose than less active ones (for respiration). The radioactive atoms cause gamma rays, which the scanner detects. More gamma rays come from parts containing more glucose.

Question 16

SB2f
1) What does spinal chord damage do?
2) What is quadriplegia?

Answer 16

1) Spinal chord damage reduces the flow of information between different parts of the body. Nerve damage in the lower spinal chord can cause loss of feeling in, and use of, the legs.
2) Quadriplegia is the loss of the use of both arms and legs, caused by damage in the neck.

Question 17

SB2h
1) What is the function of the retina?
2) What is the function of the pupil?
3) What is the function of the iris?
4) State the region of the central nervous system responsible for vision

Answer 17

1) The retina contains receptor cells which create an impulse that is sent to the brain.
2) The pupil is the dark area in the middle of the eye, which is where light enters.
3) Muscles in the iris control how much light is entering the eye. They can constrict the pupil (decrease its diameter) or dilate it (make it bigger).
4) The cerebellum

Question 18

SB2h
1) What is the function of the cornea?
2) What is the function of the lens?
3) What do the rods and cones do?

Answer 18

1) The cornea focuses light rays entering the eye onto a point in the retina to produce a clear image. It refracts (bends) light rays to bring them together.
2) The lens fine tunes the focused light. Ciliary muscles make the lens fatter to focus light from near objects and thinner to focus light from distance objects.
3) Rods and cones are receptor cells located in the retina. Cones are sensitive to the colour of light. Rods are sensitive to dim light. These cells generate impulses in sensory neurons, which lead into the brain through the optic nerve.

Question 19

SB2h
1) What is short sightedness, and how can it be corrected?
2) What is long sightedness, and how can it be corrected?
3) What is colour-blindness, and how can it be corrected?
4) What is a cataract, and how can it be corrected?

Answer 19

1) Short sightedness is when distant objects are blurry due to either the eyeball being too long, or the cornea being too curved and bending the rays more than it should. Contact lenses or lenses in glasses that use a diverging lens can correct these problems. The diverging lens refracts light rays outwards, so the light rays focus on the retina.
2) Long sightedness is when objects close to you look blurry due to either the eyeball being too short, or the cornea not being curved enough so the rays are not bent enough. Contact lenses or lenses in glasses that use a converging lens can correct these problems. The converging lens refracts light rays inwards, so the light rays focus on the retina.
3) Colour blindness is where some of the cones in the retina are not working properly, so it is difficult to see certain colours. Colour blindness cannot be corrected.
4) A cataract is when protein builds up inside the lens and makes it cloudy. This problem can be corrected by replacing the clouded lens with an artificial one.

Question 20

SB2h
1) How does the shape of the lens change to allow a person too see nearby objects clearly in normal vision?
2) How does the shape of the lens change to allow a person too see distant objects clearly in normal vision?

Answer 20

1) To focus on a near object - the ciliary muscle contracts, which slackens the suspensory ligaments. This makes the lens become thicker, and allows the light rays to refract (bend) more strongly.
2) To focus on a distant object - the ciliary muscle relax, which stretches the suspensory ligaments. This makes the lens become thin, and allows the light rays to refract light rays to refract slightly.

Question 21

SB2i
1) What are the parts of the central nervous system?
2) What is a stimulus?
3) How does the body detect stimuli, and what is done in response?

Answer 21

1) The parts of the central nervous system are: the brain and the spinal chord.
2) A stimulus is a change in your body or in the surroundings.
3) Sense organs (such as eyes and skin) contain receptor cells that detect stimuli. Receptor cells create impulses, which usually travel to the brain. The brain the processes this information and can send impulses to other parts of the body to cause something to happen (a response).

Question 22

SB2i
1) What is neurotransmission?
2) What is a sensory organ’s function and how is it adapted?
3) What are the parts of the neuron cell?
4) What is the myelin sheath and what in its function?

Answer 22

1) Neurotransmission is the transmission (travelling) of impulses and happens in neurons (nerve cells).
2) A sensory neuron’s function is to carry impulses from receptor cells towards the CNS (central nervous system). They are adapted by being very long to cover more distance.
3) The dendrites receive the impulses. After the dendrites and before the cell body is the dendron. After the cell body and before the axon terminals is the axon. The axon terminals pass impulses to other neurons.
4) The myelin sheath is a fatty layer surrounding the dendron and axon. This electrically insulates a neuron from neighbouring neurons, stopping the signal losing energy. They also speed up neurotransmission.

Question 23

SB2i
1) How does the nervous system react to stimuli?
2) What do motor and relay neurons do?
3) What is a synapse and what is its function?

Answer 23

1) When the brain coordinates a response to the stimulus, impulses are sent to effectors and these carry out an action.
2) Motor neurons carry impulses to effectors. Relay neurons are short neurons that are found in the spinal chord, where they link motor and sensory neurons. Neither of them have a dendron, only dendrites on the cell body.
3) A synapse is a small gap between two neurons. When an impulse reaches an axon terminal, a neurotransmitter chemical is released into the gap. This is detected by the next neuron which creates a new impulse. This allows impulses to be passed on from the axon terminal of one neuron to the dendrites of another neuron.

Question 24

SB2i
1) What is the function of the reflex arc?
2) What is the pathway that nervous impulses take in a reflex arc?

Answer 24

1) The function of the reflex arc is to bypass parts of the brain involved in processing information and so are quicker than responses that need processing.
2) Receptor, sensory neurone, relay neurone (in the spinal cord or an unconscious part of the brain), motor neurone, effector.

Question 25

SB2i
Explain how a signal is transmitted at a synapse and how the painkillers reduce the pain felt by the person.

Answer 25

Synapse transmission
- Neurones transmit electrical impulses the synapse is a gap between 2 neurones triggering the release of neurotransmitters which diffuse across the synapse as a chemical signal
- Neurotransmitters bind to receptors on the next neurone
- Triggering an electrical impulse in the next neurone
Painkillers
- Prevent neurotransmitters binding to receptors in the next neurone
- Electrical impulse is not triggered
- Signal is not received by the central nervous system
- Person does not feel pain