Cells and control

What is mitosis?

Cell division

Why is mitosis needed?

For growth and repair

What does haploid mean?

Half set of chromosomes

What does diploid mean?

Full set of chromosomes

What are the 6 stages of mitosis?

• Interphase

• Prophase

• Metaphase

• Anaphase

• Telophase

• Cytokinesis

What happens in interphase?

The cell spends most of its life in this phase. The DNA in chromosomes and cell organelles copy themselves ready for mitosis.

What happens in prophase?

Spindle fibres form in the cell and the nuclear membrane starts to disappear

What happens in metaphase?

Chromosomes line up in the middle of the cell

What happens in anaphase?

The chromosomes are pulled apart by the spindles to each end of the cell

What happens during telophase?

The single chromosomes arrive at opposite ends of the cell and the membranes around the chromosomes starts to form again

What happens at cytokinesis?

The cytoplasm of the cell separates and the cell membrane divides the cell into two daughter cells.

Turn over for an image of the stages of mitosis

What do red blood cells do and how are they specialised?

• They carry oxygen to cells and take carbon dioxide away

• They have a bi-concave shape which maximises their surface area to absorb oxygen

• Contain haemoglobin which can bind 4 oxygen molecules to it

What do nerve cells do and how are they specialised?

\-They send messages around the body

\-They are very long (up to 2m)

What do sperm cells do and how are they specialised?

-They carry half the genetic information

-They have a tail to swim to the egg cell

-They have acrosomes (enzymes) that let them penetrate the jelly coat of the egg cell

What do ciliated epithelial cells do and how are they specialised?

\-They move dirt from the lungs and move the ovum (egg cell) from the ovaries to the uterus

\-They have hairs to help them do this

What do Root hair cells do and how are they specialised?

\-Absorbs water from soil

\-They do not contain chloroplasts as sunlight cannot get to them, this means they have more space to contain water

What do palisade cells do and how are they specialised?

\-They absorb sunlight for photosynthesis

\-contains a large number of chloroplasts on their surface that help to absorb a large amount of sunlight

What are meristem cells in plants and what do they do?

\-Undifferentiated cells that can give rise to any other kind of cells

\-Found in places where growth takes place (shoots and roots)

What are guard cells in plants and what do they do?

\-They are found on the bottom of a leaf

\-Bends when full with water to open stomata

\-Controls water loss and gas exchange

\-Stomata opens during the day for photosynthesis

What are xylem cells in plants and what do they do?

\-Found in the middle of the stem

\-Xylem vessel consist of dead cells

\-Thick cell walls with hollow middle

\-Involved in the movement of water within a plant

What is the central nervous system made up of?

Brain and spinal cord

What are the neurone types?

Sensory, motor and relay

What are the different sense organs and what stimuli do they detect?

Eyes-Light

Skin-Pressure/temperature

Tongue-Chemicals

Nose-Chemicals

Ears-sound

What is a neurone?

A specialised nerve cell

What is a synapse?

A junction between 2 neurones

What are receptors?

Specialised cells that detect stimuli

What do sensory neurones do?

They carry the nerve impulse from the receptor to the central nervous system

What do motor neurones do?

They carry the nerve impulse to an effector

What is a stimulus?

Changes in the environment

What do effectors do?

The carry out response and are either muscles or glands

What is a nerve impulse?

the relaying of a coded signal from a nerve cell to an effector (a muscle cell, a gland cell or another nerve cell) in response to a stimulus

Put the nervous system response in order

Stimuli, receptor, sensory neurone, central nervous system, relay neurone, motor neurone and effectors

What is a reflex arc?

A reflex arc is an automatic, non-conscious and fast response to potentially harmful conditions

Why is the reflex arc useful?

Because it does not involve conscious parts of the brain making it much quicker

What is the order of a reflex arc response?

• Stimulus: touching a hot object for example

• Impulse starts at receptor cells, passed along to the sensory neurone

• Then passed along to spinal cord- in the reflex arc, the conscious part of the brain is not involved

• The relay neurone then passes impulse onto the motor neurone

• Effector receives impulse to react

• Response: lift finger away from hot object

What are neurotransmitters?

A chemical that passes across the synapse (gap between two neurones) to pass the impulse onto the next neurone

How do neurotransmitters carry chemical signals from a neurone to the target cell?

1. The nerve impulse arrives at the synapse

2. Chemical messenger (a neurotransmitter) is released into the synapse

3. The neurotransmitters diffuse across the synapse

4. When the next nerve is reached, the neurotransmitters start another impulse

Flip over for image of a sensory neurone

What is the myelin sheath and what does it do?

It is a fatty layer insulating the axon and it prevents electrical impulses from affecting the surrounding parts of the brain

Flip over for image of motor neurone

What is the brain made up of?

Billions of interconnected neurones

Flip over for image of brain

What does the cerebrum do?

It is split into two hemispheres (called the cerebral hemispheres) and is highly folded. It controls intelligence, personality, conscious thought and high-level functions, such as language and verbal memory.

(The outer layer of the cerebrum is called the cerebral cortex)

What does the cerebellum do?

controls balance, co-ordination of movement and muscular activity.

What does the medulla oblongata do?

Controls unconscious activities such as heart rate and breathing rate

What does the hypothalamus do?

Regulates temperature and water balance within the body

What is the eye?

The eye is a sense organ containing receptors sensitive to light intensity and colour.

Flip over for image of eye

What does each part of the eye do?

Cornea: Refracts light - bends it as it enters the eye

Iris: Controls how much light enters the pupil

Lens: Further refracts light to focus it onto the retina

Retina: Contains the light receptors

Optic nerve: Carries impulses between the eye and the brain

Sclera: Tough white outer layer of the eye. It helps protect the eye from injury

What are the two kinds of receptors within the eye?

Rods and cones

What do the rods in the eye do?

They are sensitive to light levels and help give us good vision in low light

What do cones in the eye do?

Cones are responsible for colour vision

What is the reflex action?

\
The amount of light entering the eye is controlled by a reflex action. The size of the **pupil** changes in response to bright or dim light. This is controlled by the muscles of the iris.

What does the eye do to focus on near objects?

 the lens becomes **thicker**, this allows the light rays to refract (bend) more strongly.

How does the eye focus on distant objects?

the lens is pulled **thin**, this allows the light rays to refract slightly.

Flip over for image explaining how the eye changes to focus on near and far objects

What is myopia and hyperopia

short sightedness and long sightedness

What problem do short sighted people have?

Someone with **short-sight** can see near objects clearly, but cannot focus properly on distant objects.

What can short sightedness be caused by?

• The eyeball being elongated - so that the distance between the lens and the retina is too great.

• The lens being too thick and curved - so that light is focused in front of the retina.

How can short sightedness be corrected?

Short-sightedness can be corrected by placing a concave lens in front of the eye, as shown in the diagrams below.

What problem do long sighted people have?

Someone who is **long-sighted** can see distant objects clearly, but they cannot focus properly on near objects.

What is long sightedness caused by?

* the eyeball being too short - so the distance between the lens and retina is too small
* a loss of elasticity in the lens - meaning it cannot become thick enough to focus (which is often age-related)

What does the lens do instead of focusing the light onto the retina for long sighted people?

the lens focuses light behind the retina instead of onto it.

How is long sightedness corrected?

Long-sightedness is corrected by putting a convex lens in front of the eye

How do contact lenses correct vison?

 **Contact lenses** – work by being in 'contact' with your eye. They float on the surface of the cornea. They work like spectacle lenses, by focusing and refracting the light.

How does laser surgery correct vision?

 reshapes the cornea surgically. Common for myopia but can be used for some hyperopia conditions.

How do replacement lens correct vision?

Implanting artificial lenses is a recent development, and can placed in front of the original lens, through a small cut in the cornea, to correct an eye defect.

What is differentiation?

When a normal, undifferentiated cell turns into a specialised cell to carry out a particular function

What is the zone of elongation in a plant?

The area where cells are dividing rapidly to make more new cells

What two ways can growth be estimated?

Change in length and change in mass

How do you read a percentile chart?

• Assume a graph is showing the weight of babies

• On a graph you will be told which line in which percentile

• If the line is the 95th percentile then 95% of babies will be under this mass

• If a baby’s weight is above the 95th percentile or below the 5th percentile it may not be growing properly

• If a baby’s mass drops by two or more percentiles over a year, it may not be growing properly

What are stem cells?

Unspecialised cells that can differentiate into any other cells

What are embryonic stem cells?

Stem cells taken from embryos in early stages of development which can differentiate into any other type of cell

What are adult stem cells?

• Stem cells taken from differentiated tissue such as bones or skin

• They divide to replace damaged cells

What are the uses of embryonic stem cells?

• Replacing or repairing brain cells to treat people with Parkinson’s disease

• Replaces damaged cells in the retina of eye to treat some kinds of blindness

• Growing new tissues in the lab to use for transplants or drug testing

What are the uses of adult stem cells (from bone marrow)?

• Treatment of leukaemia (cancers of the white blood cells, starting in the bone marrow)

• Potentially growing new tissues that are genetically matched to the patient

What are the advantages and disadvantages of using embryonic stem cells?

• Easy to extract from embryo

• Produce any type of cell

• Embryo destroyed when cells removed- some people think embryos have a right to life

What are the advantages and disadvantages of using adult stem cells?

• No embryo destroyed so no ethical issue

• If taken from the person to be treated, will not cause rejection by the body

• Produces only a few types of cell

What advantage do all kinds of stem cells have?

They replace faulty cells with healthy cells, so the person is well again

What is the risk for all kinds of stem cells?

Stem cells may not stop dividing, causing cancer

What is stem cell rejection?

When a donors stem cells are not accepted by the patients body, the immune system attacks the stem cells

What happens in a CT scan?

• The patient is give a radioactive tracer which allows different parts of the brain to show up

• A CT scan is carried out, taking many different X-rays of the skull and brain from different angles

• A computer puts all these things together to give a three- dimensional image

What happens in a PET scan?

• The patient is given a small amount of a radioactive form of glucose

• This travels to parts of the body where respiration is happening rapidly

• This shows up as changes in parts of the body such as the brain that might indicate damage or disease

• The scanner detects the radioactivity and builds up images showing where the radioactive tracer is most concentrated

How does breaking your spinal cord cause you to be paralysed?

• Nerve impulses to and from the lower part of the body pass through the spinal cord

• If this is damaged then there is no way the nerve impulse can be carried from the brain to lower parts of the body

What is the difference between the spine and spinal cord?

The spinal cord is made of nerves and this lies inside the spine for protection

Why is damage to the nervous system so difficult to treat?

All of the separate parts are well protected

Why is the brain so hard to treat?

• Protected by the skull

• Capillaries that supply the brain are not as leaky as normal capillaries- this is called the blood-brain barrier and it makes it difficult to get medicines into the brain

• Neurones are specialised so they cannot divide to replace damaged cells

Why is the spinal cord so hard to treat?

• It is protected by the spine

• Neurones are specialised so they cannot divide to replace damaged cells

Why can treating a brain tumour with radiotherapy be dangerous?

Radiotherapy can not only remove the tumour but also damage healthy nerve cells

What is cataracts and how can it be treated?

• When the lens becomes cloudy

• It is caused when proteins in the lens of the eye break down and clump up together

• This causes a blurred image

• It can be treated by replacing the cloudy lens with an artificial lens

What is colour blindness caused by?

• A normal retina contains three types of cones that can detect blue, green and red light. The colour of an image is detected by how much each type of cone is stimulated

• In colour blindness, at least one type of cone is missing or does not work properly

• This occurs mostly in males

• In red-green colour blindness, either red or green cones are missing, and the person cannot distinguish between the two colours