Name the two stages of the cell cycle
Interphase and mitosis
List the five stages of mitosis in order
- prophase
- metaphase
- anaphase
- telophase
- cytokinesis
Describe what happens during interphase
The stage when the cell prepares itself for the process of cell division, and DNA replication takes place. The cell also makes more of its sub-cellular structures, and increases in size
Describe what happens during each stage of mitosis
Prophase: the nucleus starts to break down and spindle fibres appear
Metaphase: the chromosomes line up across the middle of the cell
Anaphase: the separated chromosomes move away from each other
Telophase: the chromosomes arrive at opposite ends of the cell and the nucleus membrane reforms
Cytokinesis: the cytoplasm of the cell is separated as the cell membrane is pinched to divide the cell into two daughter cells
Why is mitosis important for an organism?
It is a process of producing genetically identical, diploid cells, needed for growth
What do we call cells that have one copy of each chromosome?
Haploid
Name three examples of a cell with only one copy of each chromosome
Gametes: egg, sperm, pollen
What do we call cells that have two copies of each chromosome?
Diploid
Name an example of a cell with two copies of each chromosome
Any body cell (eg. Muscle, epithelial, nerve etc.)
Fruit flys have four types of chromosomes. How many chromosomes are in a diploid fruit fly cell?
8
Explain why the number of mitochondria in a cell doubles during interphase
So each daughter cell has enough mitochondria/ same number of mitochondria as parent cell
What do we call the offspring from asexual reproduction?
Clones
What are spindle fibres and what is their function?
Filaments formed in a cell during mitosis, which help to separate chromosomes
Give a benefit of asexual reproduction
- produces clones
- doesn’t need two parents
- fast method of producing offspring
Give a disadvantage of asexual reproduction
- does not provide variation, so a whole population could get killed by one disease
Describe how mitosis produces genetically identical, diploid cells
The cell copies each chromosome to produce two sets. Each set of chromosomes move to opposite sides of the cell. The cell then splits into two cells, each with a full set of identical chromosomes
Why is each plantlet that grows along a strawberry runner a clone?
Because they are genetically identical to the parent plant/ have the same chromosomes (/DNA/genes) as the parent plant
How can cancers grow?
The cell cycle goes out of control
Describe what a ‘crown gall tumour‘ on a rose plant will look like?
A lump (often brown) on the stem
Explain how crown gall tumours develop
There is a change to the cells that causes rapid and uncontrollable cell division
What is the definition of growth?
An increase in size due to an increase in the number or size of cells
What are percentile curves used for?
The graph shows the expected rate of growth of babies of different birth weights and is used to check that a child‘s growth is normal
What are the three zones of growth in plants?
- zone of cell division (meristem)
- zone of elongation
- zone of differentiation
Name the two types of stem cells in animals
Embryonic stem cells and adult stem cells
Describe the differences between the two types of animal stem cells
Embryonic stem cells can produce any type of specialised cell whilst adult stem cells can only produce the type of specialised cell that is in the tissue around them
Give three advantages of using stem cells to treat people
(1) no need to take anti-rejection drugs because cells are genetically identical
(2) no need to find a donor
(3) no need for tissue typing
Give some disadvantages of using stem cells to treat people
(1) the stem cells may cause cancer if they continue to divide inside the body after they have replaced the damaged cells
(2) cultured stem cells could be contaminated with viruses which would be transferred to a patient
(3) no guarantees that the therapy will be successful
(4) lack of stem cell donors
(5) hard to obtain and store a person‘s embryonic stem cells - need to be collected near the start of the pregnancy
What are the ethical problems of using stem cells to treat people or during research?
- one source of embryonic stem cells is unused embryos produced by ‘in vitro fertilisation‘ (IVF)
- is it right to create embryos for therapy, and destroy them in the process?
- embryos could come to be viewed as a commodity (item), and not as an embryo that could develop into a person
- when should an embryo be regarded as, and treated as, a person?
What are plant stem cells called?
Meristem cells
Name two parts of a plant where stem cells can be found
- roots
- shoots
What are chromatids?
The product produced when chromosomes replicate
What cells is mitosis unlikely to occur in?
- sperm/egg cell (gametes)
- red blood cell
- lymphocyte
Which structures of a flowering plant give rise to potatoes?
A potato is a tuber formed at the end of an underground stem
Which structures of a flowering plant give rise to the fleshy scales of an onion?
Onion scales are modified leaves containing a food store
In the process of tissue culture in plants, what is needed to induce the formation of a complete plant, in addition to a growth medium with nutrients?
The appropriate plant growth substances (‘hormones‘) would need to be added
List four stimuli which can be detected by the skin
- heat
- cold
- touch
- pressure
How do we become aware of a stimulus?
Nerve impulses travel from a receptor to the brain
Name the transparent outer layer found at the front of the eye
Cornea
What is the retina?
It is the layer at the back of the eye that contains light receptor cells
What is the pupil?
It is the hole in the centre of the eye through which light enters
What is the iris?
The part of the eye that contains muscles that control the size of the hole in the centre of the eye
Name the muscles that control the shape of the lens
Ciliary muscles
Name the nerve that takes information from the eye to the brain
Optic nerve
What happens to the optic nerve when a bright light shines in the eye?
Impulses travel in the optic nerve
When a bright light shines in the eye, do the radial fibres in the iris contract?
No, the circular muscles in the iris contract to make the pupil smaller (in dim light the radial muscles contract to make the pupil larger)
What responds when a bright light shines in the eye?
The retina
What is the cause of the blind spot in the field of vision?
There are no sensory cells in the blind spot
Which parts of the eye refract the light to form an image on the retina?
The curved surface of the cornea, and the lens
What do you understand by the term ‘accommodation‘?
Accommodation is the way the eye can focus either near or distant objects to form a sharp image on the retina
What part does the lens play in the the process of accommodation?
The lens is made thinner so that light from a distant object is refracted less, or fatter so that light from a close object is refracted more
What happens to the ciliary muscle and lens for an eye to focus on a distant object?
The ciliary muscle relaxes and the lens gets thinner
What happens to the ciliary muscle and lens for an eye to focus on a near object?
The ciliary muscle contracts and the lens gets thicker
What is a cataract?
A cloudy patch on the lens
Explain why cataracts cause blurred vision
Cataracts stop light from entering the eye as normal so less light reaches the retina
What treatment is offered to people with cataracts?
The cataract lens can be surgically removed and is replaced by an artificial lens. Only one eye is done at a time so that the person can have vision
What kind of eye defect can give rise to short-sightedness?
Long eyeballs, large eyeballs, too powerful a lens, or a combination of these defects
What are the three names for the lenses that correct long-sightedness?
- converging (oval)
- convex (oval)
- meniscus (convex one side, concave the other side)
Name the nerve fibres which carry impulses from the sense organs to the central nervous system
Sensory
How can we tell which part of the body a sensory nerve impulse comes from?
Each part of the body is connected to its own region of the brain
What is the function of an axon?
To carry the nerve impulse away from the cell body
Describe the transmission of information from the stimulus of rods and cones in a dog‘s eye when it sees a cat, to the dog‘s muscles (via the CNS) as it responds and runs after the cat
Rods and cones (stimulus) —> sensory neurone/ optic nerve —> CNS (relay neurone) —> motor neurone —> muscle cells (response)
What is a reflex?
A fast, automatic response to a stimulus (does not involve brain)
Explain why neurones can deliver information very quickly
The signal is transmitted by electrical impulses
Explain why doctors use electrical impulses to stimulate different parts of the brain
To find out what different parts of the brain do
How do nerve impulses travel from one nerve to another?
The neurotransmitter is released by the axon of one neurone and diffuses across the gap to the dendrite of the other neurone. The neurotransmitter is absorbed into the dendrite which sets off an electrical impulse down the neurone.
