Topic 2 - Cells and Controls

Question 1

SB2a - How are tumors formed?

Answer 1

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

Question 2

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

Answer 2

• 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 3

SB2a - Describe stages of mitosis

Answer 3

Mitosis

• Interphase
  
  • Copies of the chromosomes are formed in the nucleus
• 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 (In plants, a cell wall is also formed)

Question 4

SB2a - What are the products of mitosis called?

Answer 4

Daughter Cells

Question 5

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

Answer 5

Unicellular organisms

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

SB2a - Why is mitosis important in organisms?

Answer 7

• Asexual Reproduction
• Growth
• Repairing damage
• Cell Replacement

Question 8

SB2b - Define growth.

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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 11

SB2b - What is cell differentiation?

Answer 11

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

Question 12

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

Answer 12

• large vacuole - stores absorbed water
• long projection - increases area for absorption
• thin cell - allows minerals to pass easily into the cell by reducing the area they have to transport

Question 13

SB2c - How are xylem cells specialised for their function?

Answer 13

• They have thick walls containing lignin, giving the xylem a rigid and strong structure
• The cells rae dead - so all water carried is transported and not used up by the xylem itself
• 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 meristems?

Answer 14

• 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 15

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

Answer 15

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

Question 16

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

Answer 16

• 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 17

SB2d - What are the problems with using stem cells in medicine? (6)

Answer 17

• 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
• Embryonic stem cells pose an ethical issue
• Potential long-term side effects are unknown
• Stem cells could be contaminated during the operation, so when transferred into the patient it only makes them sicker

Question 18

SB2d - What is an embryonic stem cell?

Answer 18

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

Question 19

SB2d - What the ethical risks of using stem cells? (2)

Answer 19

1. Embryos that were used to provide stem cells are destroyed which is seen as unethical and a waste of potential human life
2. May lead to the reproductive cloning of humans

Question 20

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

Answer 20

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

Question 21

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

Answer 21

Their cells remain able to differentiate freely throughout their lives.

Question 22

SB2d - What are the benefits of using stem cells in medicine ? (4)

Answer 22

1. Treating damage or disease
2. Treating otherwise untreatable diseases
3. Growing organs for transplants
4. Used in scientific research

Question 23

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

Answer 23

• 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 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

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

Answer 25

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

Question 26

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

Answer 26

Neurones

Question 27

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

Answer 27

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

Question 28

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

Answer 28

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

Question 29

SB2f - How does a CT scan work?

Answer 29

* 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 30

SB2f - How does a PET scan work?

Answer 30

* 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 31

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

Answer 31

* 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 32

SB2f - Why is spinal cord damage so dangerous?

Answer 32

* 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 33

SB2g - What are the different types of neurones and their functions?

Answer 33

* Sensory Neurones - carry impulses from receptor cells to CNS * Motor Neurones - carry impulses from the CNS to effector organs * Relay Neurones - found in the spinal cords, link motor & sensory

Question 34

SB2g - How does your body communicate?

Answer 34

Using electrical signals called impulses

Question 35

SB2g - Describe the structures in a sensory neurone * Dendrites * Cell Body * Dendron * Axon * Myelin Sheath * Axon Terminal

Answer 35

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 36

SB2g - What are sense organs?

Answer 36

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

Question 37

SB2g - What is the spinal cord?

Answer 37

* A long, thin structure composed of neurones that extends from the medulla oblangata to the spine

Question 38

SB2g - What makes up the nervous system?

Answer 38

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

Question 39

SB2h - Describe the structure of the eye.

Answer 39

* 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 40

SB2h - How does the eye vary with the distance of the object?

Answer 40

**_Far_** * Ciliary Muscles Relax * Suspensory Ligaments Tighten * Lens becomes less convex * Light is refracted less * Light is focused onto the retina **_Close_** * Ciliary Muscles Contract * Suspensory Ligaments Slack * Lens becomes more convex * Light is refracted more * Light is focused onto the retina

Question 41

SB2h - What is a cataract?

Answer 41

* 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 42

SB2h - What is colour-blindness?

Answer 42

* 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 43

SB2h - What is myopia and hyperopia? * Causes * Treatment

Answer 43

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 44

SB2h - What is the function of the iris?

Answer 44

* To control the size of the pupil to alter how much light enters the eye

Question 45

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

Answer 45

* 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 46

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

Answer 46

* 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)