SB2 - Cells and Controls ✓

Question 1

SB2a - When a regular human body cell divides, what is this process called, and how does it occur?

Answer 1

Mitosis

• Prophase
  
  • The nucleus starts to break up and spindle fibres appear.
• Metaphase
  
  • The chromosomes are lined up on the spindle fibre across the middle of the cell
• Anaphase
  
  • The chromosome copies are separated and moved to either side of the cell
• Telophase
  
  • A membrane forms around each set of chromosomes to from a nuclei
• Cytokeniesis
  
  • Cell surface membrane forms separating the two cells (Implants, a cell wall is also formed)
• Interphase
  
  • Copies of the chromosomes are formed in the nucleus
• The cycle repeats

Question 2

SB2a - What are the products of mitosis called?

Answer 2

Daughter Cells

Question 3

SB2a - What type of organisms do not require mitosis to occur?

Answer 3

Unicellular organisms

Question 4

SB2a - How many types of chromosones are in a human cell and what is it called when these are alone or paired up?

Answer 4

• 23 types of chromosomes.
• When they are paired up to have 46 chromosomes this is a diploid cell and a haploid cell only has 23 chromosomes.
• Gametes are haploid cells while all other cells in a human are diploid.

Question 5

SB2a - How are tumors formed?

Answer 5

• When cells mutate, they can become cancer cells.
• This means that they will divide even when they don’t require to divide.

Question 6

SB2a - Why does asexual reproduction require mitosis?

Answer 6

• As asexual reproduction only needs one parent, the offspring will have the same DNA as the parent.
• As the offspring are clones and their chromosomes are identical, their cells are formed by mitosis.

Question 7

SB2b - Define growth.

Answer 7

The increase in size as a result of an increase in size of or numbers (due to cell division) of cells.

Question 8

SB2b - How is the growth of a baby monitored and how does this work?

Answer 8

Using a percentile growth curve:

• This graph has many lines showing you how a babies conditions compare to the average.
• The healthiest position would be at 50% as half of the population is above or below you.
• Being above 98% or below 2% is reason for concern as only 2% of the population is above or below you.

Question 9

SB2b - What is cell differentiaiton?

Answer 9

When a less specialised cell is changed to become a specialised one.

Question 10

SB2b - How are red blood cells specialised for their purpose?

Answer 10

• Biconcave shape means more surface area for oxygen diffusion.
• No nucleus means more space for red haemoglobin molecules and carry more oxygen

Question 11

SB2c - What are the meristems?

Answer 11

• A group of cells near the end of each shoot that allow plants to continue growing throughout their lives.
• They divide rapidly and the cells are elongated and differentiated.

Question 12

SB2c - How are root hair cells specialised for their function?

Answer 12

• Root hair cells have hair to increase their surface area to allow them to absorb water more effectively.
• They also don’t contain chloroplasts (as they are underground and can’t photosynthesise)

Question 13

SB2c - How are xylem cells specialised for their function?

Answer 13

• They have thick walls containing lignin.
• This causes the cells to die
• As the cells die, the end walls connecting them break away, meaning the cells form a long tube
• Along with the fact that they have no internal structure at all (nucleus, chloroplasts etc.) this makes it easier to transport water and minerals.

Question 14

SB2c - What are the zones of differentiation elongation and cell division?

Answer 14

• D: Where cells are specialised
• E: Where cells are elongated (vertically extended)
• CD: Where rapid mitosis occurs (Meristems)

Question 15

SB2d - What is an embryonic stem cell?

Answer 15

A cell in an early stage embryo that is not specialised and can differentiate to form any type of specialised cell.

Question 16

SB2d - Where can adult stem cells be found and how are they different to embryonic stem cells?

Answer 16

Adult stem cells can be found in most tissues including bone marrow but can only differentiate to cells in the tissue around them .

Question 17

SB2d - How can stem cells be used to treat lukemia?

Answer 17

• A patient’s bone marrow is destroyed using radiation
• Adult stem cells are inserted into the patient
• The stem cells will differentiate specialise and divide to form new blood cells and bone marrow

Question 18

SB2d - What are the problems with using stem cells in medicine?

Answer 18

• If stem cells continue to divide, it can cause a cancerous tumour to form
• Stem cells of one person can be rejected by the immune system of another

Question 19

SB2d - Why don’t plants have adult stem cells?

Answer 19

Their cells remain able to differentiate freely throughout their lives.

Question 20

SB2e - What type of cells is the brain mostly made up of?

Answer 20

Neurones

Question 21

SB2e - What are the three major structures of the brain, and what are each of their functions?

Answer 21

• Cerebral cortex: Main functions and control such as memories language etc.
• Cerebellum: Controls balance and movement
• Medulla oblongata: Controls heart and breathing rate

Question 22

SB2e - How did Phineas Gage’s accident prove what the cerebral coretex is used for?

Answer 22

• Phineas gage had a metal rod stuck inside his brain
• It was through his cerebral cortex
• He was still able to walk, but his personality changed
• This shows that this part of the cerebral cortex controls emotions and personality but not movement or breathing/heart rate

Question 23

SB2e - Why may musicians have larger/more developed cerebellums?

Answer 23

So can develop and have more control over their fine movements and timing coordination

Question 24

SB2e - The medulla oblongata controls reflexes. What does this mean about its connections?

Answer 24

It connects the brain to the rest of the CNS

Question 25

SB2f - During brain surgery, what may be don to investigate roles of the brain?

Answer 25

Probing with electricity (electrodes) means that doctors can control the activity of different parts of the brain

Question 26

SB2f - How does a CT scan work?

Answer 26

* A CT scan involves an x-ray beam moving in a circle around the head. * It produces images that are slices of the brain. * Computers can layer and build these up to produce an image

Question 27

SB2f - How does a PET scan work?

Answer 27

* Radioactive glucose is injected into the body. * More active cells take in more glucose. * The PET scan scans for where the most radioactivity is coming from showing the levels of activity in the brain.

Question 28

SB2f - Why is spinal cord damage so dangerous?

Answer 28

* Damage to the spinal cord can sever the connection between your brain and the rest of your body. * This can loose to the loss of control of limbs such as quadripalegia.

Question 29

SB2f - Why does chemotherapy not always work for brain tumors?

Answer 29

* Chemotherapy involves sending chemical substances through blood to actively kill tumours * The brain has a natural filter called the blood-brain barrier which blocks out foreign substances in the brain * Additionally, chemotherapy can harm healthy cells

Question 30

SB2g - What makes up the nervous system?

Answer 30

* The CNS (Central nervous system): * The brain * The spinal cord * Nerves

Question 31

SB2g - How does your body communicate?

Answer 31

Using electrical signals called impulses

Question 32

SB2g - What are sense organs?

Answer 32

Organs that contain receptor cells which will cause the body to have a response to a stimulus. e.g. eyes, ears etc.

Question 33

SB2g - Describe the sturcture of a sensory neuron.

Answer 33

* Dendrites receive the electrical impulses from the receptor * This is passed on through the dendron and the axon * Axon terminals at the other end allow the electrical impulse to be passed on * The cell body containing the nucleus is between the dendron and axon * The cell is covered in fatty layer called the myelin sheath * This insulates the cell meaning there are no electrical jumps to other cells speeding up neurotransmission

Question 34

SB2h - Describe the structure of the eye.

Answer 34

* There is a clear covering called the cornea covering the eye which refracts most of the light * Below this are the iris and the pupil * CIllary muscles alter the shape of the eye (constricting or dialating it) * A lens to fine tune the light refraction * At the back is the retina containing rods (detect light levels) and cones (detect colour. Don't function well in dim light) * This is passed onto optic nerves which pass electrical impulses to the brain * Refracted light should meet at the retina

Question 35

SB2h - What is myopia and hyperopia?

Answer 35

Myopia is short sightedness (Can see close): * This is when light focuses too early (before the retina) * The eyeball is too long. * This can be fixed with a diverging lens. Hyperopia is long sightedness (Can see far): * This is when light hasn't focused by the time it reaches the retina. * The eyeball is too short. * This can be fixed with a converging lens

Question 36

SB2h - What is a cataract?

Answer 36

* Protein build up in the lens can cause it to become cloudy, clouding your vision. * This can be corrected by replacing the lens with a plastic one

Question 37

SB2h - What is colour-blindness?

Answer 37

* When the cone cells in your eye don't properly detect colour * The most common form of this is red-green colour blindness * This cannot be corrected

Question 38

SB2i - Describe the reaction process (not reflex arc).

Answer 38

* The receptor cells in your sensory organs respond to a stimulus * They send a neurotransmission which using neurones, travels to your brain * Your brain decides what action to take and sends a neurotransmission using neurones to send a message to an effector e.g. muscle contracting

Question 39

SB2i - Describe the roles synapses play in the reflex arc. (include the three types of neurones)

Answer 39

* The receptor passes on an impulse to the sensory neurone * The sensory neurone reaches a 'junction' called a synapse. It contains a tiny gap * Once it reaches here, a chemical (neurotransmitter) is released passing on the impulse to the relay neurone in the spinal cord * The relay neurone reaches another synapse where it releases more neurotransmitters to pass it on to a motor neurone * The motor neurone reaches the effector where it causes a response to take place (e.g. muscle contracting)