cells and control

Question 1

Describe mitosis as part of the cell cycle, including the stages
interphase, prophase, metaphase, anaphase and telophase and
cytokinesis

Answer 1

interphase - before cell divides its DNA is spread into long stings, before dividing the cell has to grow and increase amount of subcellular structures. duplicates its DNA copied into Xshaped chromosomes which are duplicates of each other

prophase - chromosomes condense, membrane around nucleus breaks down and chromosomes lie free in cytoplasm

metaphase - chromosomes line up at centre of cell

anaphase - spindle fibres pull chromosomes apart then to opposite end of cell

telophase - membranes form around each sets of chromosomes which become the nuclei of the 2 new cells, the nucleus has divided

cytokinesis - before telophase ends, cytoplasm and cell membrane divide to from 2 separate cells

Question 2

Describe the importance of mitosis in growth, repair and
asexual reproduction

Answer 2

mitosis is used to grow or replace cells that have been damaged
some organisms use mitosis to reproduce in asexual reproduction

Question 3

what is the division of a cell by mitosis

Answer 3

• produces two identical daughter cells
  
  • these have identical sets of chromosomes in the nucleus to the parent cell
    - results in formation of two genetically identical diploid body cells

Question 4

Describe cancer as the result of changes in cells that lead to
uncontrolled cell division

Answer 4

cancer can occur when cells divide uncontrollably,
which could happen if one of the genes that control cell division
when cells divide uncontrollably this can result in a mass of abnormal cells called a tumour,
if the tumour invades and destroys tissue this is called cancer

Question 4

what is cell differentiation

Answer 4

cell differentiation = the process by which a cell changes to become specialised for its job. so its multicellular organism can work more efficiently

Question 5

describe growth in animals

Answer 5

happens by cell division.
when animals are young their growing so their cells divide at a fast rate, but mostly when your older cell division is for repair to replace damaged or old cells.
so in most animals cell differentiation is lost at an early stage

Question 6

describe growth in plants

Answer 6

cell division, elongation and differentiation
growth in height is mainly elongation,
cell division happens in tips of roots (meristems)
plants often grow continuously so they differentiate to develop new parts

Question 7

what is cell elongation

Answer 7

when plant cells expand making the cell bigger and so making the plant grow

Question 8

Explain the importance of cell differentiation in the development
of specialised cells

Answer 8

cell differentiation produces specialised cells so the specialised cells can allow multicellular organisms to work more effectively
stem cells can differentiate into specialised cells as stem cells divide by mitosis to become new cells which then differentiate

Question 9

how do percentile charts monitor growth

Answer 9

1. growth charts are used to assess a child’s growth over time so that an overall pattern in development can be seen as well as any problems highlighted
2. the chart shows a number of percentiles, ex 50th percentile shows mass that 50 babies will have reached
   ex if a babies head is above the top percentile line or below the bottom percentile line or if there is an inconsistent pattern then doctors might investigate

Question 10

Describe the function of embryonic stem cells, stem cells in
animals and meristems in plants

Answer 10

embryonic - human embryonic stem cells are the most versatile because they can develop into any cells.

stem cells in animals - adults can also have stem cells, ex finding them in bone marrow, these aren’t as versatile as embryonic stem cells . adult stem cells can be used to replace damaged tissue

stem cells in meristems in plants - the only cell in plants that can divide by mitosis are found in the meristem, meristem is found is parts of plant that are growing ex roots and shoots
meristems produce unspecialised cells that are able to form can cell type for as long as the plant lives

Question 11

Discuss the potential benefits and risks associated with the use
of stem cells in medicine

Answer 11

benefits
- stem cells can create specialised cells to replace cells that have neem damaged by a disease or injury
- stem cells have the potential for new cures as stem cells have already been used to cure some diseases

risks - tumour development - stem cells divide quickly, if at uncontrollable rate this can develop a tumour
- disease transmission - viruses live inside cells, if donor stem cells are infected then the virus could be passed on
- rejection - patients body may recognise these new cells as being foreign and so may trigger an autoimmune response to get rid of them. (the patient can take drugs to supress this which could lead to them being more susceptible to diseases)

• ethical issues - early human embryos used shouldn’t be used for experiments when each one has a potential for a human life

Question 12

explain the structure and the function of sensory neurones

Answer 12

sensory neurones
- one long dendron that carries nerve impulses from receptor cells to cell body located in middle of neurone
- one short axon that caries nerve impulses from cell body to CNS

Question 13

explain the structure and the function of motor neurones

Answer 13

motor neurones
- many short dendrites carry nerve impulses from CNS to the cell body
- one long axon that carries nerve impulses from the cell body to effector cells

Question 14

explain the structure and the function of relay neurones

Answer 14

relay neurones
- many short dendrites carry nerve impulses from sensory neurones to cell body
- an axon that carries nerve impulses from cell body to motor neurones

Question 15

explain the structure and the function of sensory receptors

Answer 15

groups of cells that can detect a change in you environment (stimulus), a stimulus is detected by receptors and the information is converted to nervous (electrical) impulses and sent to sensory neurones to the CNS.

Question 16

explain the structure and the function of synapses in the transmission of electrical impulses

Answer 16

synapse = a connection between two neurones
nerve signal is transferred to chemicals called neurotransmitters which diffuse across the gap
neurotransmitters set off electrical signals in next neurone
transmission of a nervous impulse is very fast but is slowed down at the synapse because the diffusion of neurotransmitters across the gap takes time

Question 17

explain the structure and the function of an axon, dendron, myelin sheath

Answer 17

axon = carries nerve impulses away from cell body
dendron = carry nerve impulses towards the cell body
myelin sheath = acts as an electrical insulator speeding up electrical impulses, often surround axons

Question 18

explain the structure and the function of neurotransmitters

Answer 18

• a chemical that transferrers nerve signals

Question 19

explain the structure and the function of relay neurones in the CNS

Answer 19

• impulses travel through CNS along relay neurones

Question 20

Explain the structure and function of a reflex arc including
sensory, relay and motor neurones

Answer 20

reflex arc = passage of information in a reflex (from receptor to effector)
1. stimulus detected by receptors, impulses sent along a sensory neurone to a relay neurone in the CNS
2. when impulses reach a synapse between the sensory and relay neurone they trigger neurotransmitters to be released, these cause impulses to be sent along relay neurone
3. when impulses reach synapse between the relay neurone and the motor neurone, same thing happens. neurotransmitters are releases and cause impulses to be sent along the motor neurone
4. impulses travel along motor neurone to the effector
5. muscle contract
6. you don’t spend time thinking about a response so its quicker than normal responses

Question 21

what is a synapse

Answer 21

connection between two neurones