B2 Biology

Question 1

what are the cell cycle steps ?

Answer 1

1) growth - increases in size and amount of sub cellular structures (e.g. mitochondria and ribosomes)

2) DNA replication + Mitosis - cell division where the 2 daughter cells recieve the same amount of chromosomes

3) Division (cytokinesis) - cytokinesis is only the division of cytoplasm in animal cells.

Question 2

how do organisms grow ?

Answer 2

cell growth and division

Question 3

Mitosis

Answer 3

• produces 2 genetically identical daughter cells , with identical sets of chromosomes in the nucleas with that of the parent cell

Question 4

steps of Mitosis ?

Answer 4

Prophase - nuclear membrane breaks down, chromosomes condense and spindle fibres appear

metaphase - chromosome attach to the spindle fibres and meet in the middle of the cell

Anaphase - chromosome copies are pulled to the top and bottom of the cells

Telephase - nuclear membrane is recreated around each set of chromosomes

Question 5

plant growth

Answer 5

in the end of each shoot there is a group of cells called meristems. these cells allow the plant to continue growing throughout their life. they are able to produce any type of specialized cell.

cells which have been made using mitosis are made into diffrent specialized cells this process is called differentiation.

Question 6

stem cells -

Answer 6

• stem cells are able to divide infinitely using daughter cells
• can differentiate into any specialised cells
• example: when a sperm cell meets an egg cell it forms a zygote cell (lots of these form an embryo which can differentiate into any specialized cells to form a fetus.

when people have grown up certain stem cells like bone marrow can only differentiate into certain cells like blood cells.

Question 7

what does the cerebral cortex do?

Answer 7

responsible for consciousness, intelligence, memory and language aswell as our senses

Question 8

what does cerebellum do ?

Answer 8

responsible for controlling the ballance and muscle coordination

Question 9

what does the Hypothalamus do ?

Answer 9

controls body tempreture and sends signals to the sweat glands to cool the body down if its too hot to stop enzymes from denaturing.
it also sends signals to the pituitary gland

Question 10

what does the medulla Ob (in the brain stem) do ?

Answer 10

controls unconscious activities like breathing and the heart beating

Question 11

how do scientists study the brain ?

Answer 11

they most commonly nowadays use PET, MRI and CT scans. this is because they can identify where there is a problem quickly and what the possible problem is

Question 12

what do CT, MRI and PET scans do ?

Answer 12

CT - used to see which part of the brain is damaged
PET & MRI - good at seeing the underlying activity in the brain. for example in an MRI scan if you are shown images that make you sad it will show certain parts of your brain brighter than others.

Question 13

Why is treating the brain so difficult ?

Answer 13

there is a wide range of things that can go wrong such as:

. Tumours
. infections
. trauma

the fact that it is encased in our skull and surrounded by soft tissue it makes it very difficult to fully fix everything operated on

it is also difficult to fix things with chemicals and medicine because we still dont fully understand the brain

Question 14

how does chemotherapy work?

Answer 14

• chemicals taken into the body through the blood cause DNA damage to rapidly dividing cells like Tumour cells

Question 15

what is Radiotherapy?

Answer 15

high energy X- rays can be used to damage and kill tissue, especially those which are rapidly dividing
the gamma rays can damage other tissues that they pass through

Question 16

what are sensory neurons ?

Answer 16

• carry information like changes in tempreture from our body to our brain

once the Nervous system has decided what to do with the information, it sends out Motoneurons back to the body to the ‘effectors’ (muscles or glands) to contract or release or release hormones

all this combined is called a reflex arc

Question 17

what dies the cornea in the eye do?

Answer 17

• causes all the light that comes into the eye to refract, normally perfectly onto the retina but sometimes it dosent meaning people can be short or long sited, glasses refract the light so it refocuses perfectly onto the retina

Question 18

what are photoreceptors?

Answer 18

• millions of small light sensitive cells in the retina

Question 19

why do Neurons have long Branches ?

Answer 19

too allow them too pass messages from one Neuron to a connected Neuron

Question 20

What is a Synapse ?

Answer 20

a connection between the Neurons.
whenever an electrical impulse is felt between neurons then it releases chemicals which allow the impulse to jump across

Question 21

How does the Brain recieve information ?

Answer 21

• messages are conveyed through sensory neurons to the brain
• the messages being sent come from receptors in our skin all over the body
• Once our brain has recieved the information it makes a decision and sends another message through motor neurons to our muscles with instructions (effectors)

A reflex arc is the same apart from the neurons go to your spinal cord

Question 22

where are the cornea and Iris Located

Answer 22

the very front of the Eye

Question 23

what 2 parts of the eye refract light?

Answer 23

the Cornea and the lense

Cornea - just refracts light

Lense - also refracts light but can change shape depending on how far the light needs to refract to hit the Retina

Question 24

The retina is made up of what 2 cell types?

Answer 24

Cone cells - cone cells which are sensitive to the colour of the light, this allows us to see colour but they dont work well at low light levels

Rod Cells - more sensitive to light than cone cells but cant tell colour which is why we always see balck and white when its dark

Question 25

What is the Iris Reflex ?

Answer 25

controls the size of your pupil depending on how much light enters your eye
this means youre eye dosent get damaged by light

Question 26

what muscles control the reflex arc ?

Answer 26

the Circular and Radial muscles

• When the eye wants to let more light in the circular muscles relax and the radial muscles
  Contract and when the eye wants to let less light in the circular muscles contract and the
  Radius relax.