Topic 2 - Cells and Control

Interphase

Grows in size, makes more sub-cellular structures and DNA replicates

Mitosis

Nucleus divides

Prophase

Each DNA molecule coils up, which causes the chromosomes to become shorter, fatter, and more visible. The nucleus membrane then breaks down and spindle fibres form

Metaphase

The chromosomes line up on the spindle fibres at the equator of the cell

Anaphase

Each original chromosome is separated from its copy and they are pulled to opposite poles of the cell

Telophase

The two sets of chromosomes reach the poles and become longer and thinner again. The nuclear membrane reforms

Cytokinesis

Cell divides, where the cytoplasm and cell membrane of the parent cell divide to produce two separate daughter cells

Importance of mitosis

Growth by increasing the number of cells, repair by replaces cells, asexual reproduction that only involves one parent and does not involve sex cells

Cancer

Changes in cells that can cause a cell to divide uncontrollably

Benign tumour

Contained in one area, usually within a membrane, and does not spread to other parts of the body

Malignant tumour

Spread in the blood to different parts of the body, where they can start secondary tumours

Differentiation

The process by which a less specialised or unspecialised cell develops and changes to become specialised

Specialised cell

Adapted with features to perform a particular function

Cell elongation

The process of plant cells increasing in size

Meristems

A group of cells near the end of each shoot and root - undifferentiated and divide rapidly

Stem cells

Have not undergone differentiation to become specialised and can divide repeatedly to make more stem cells, or can differentiate to become specialised cells

Embryonic stem cells

Found in early embryos and can differentiate into any cell type

Adult stem cells in animals

Found in animal bodies and can differentiate into some cell types, but not all - for growth and to replace old or damaged cells

Adult stem cells in plants

Found in plant bodies, in meristems, and can differentiate into all types of plant cells at any time during the life of the plant

Potential for stem cells

Treating patients with currently untreatable conditions, growing organs for transplants, medical research

Medical treatments with stem cells

Type 1 diabetes, Parkinson’s disease

Clinical issues with using stem cells

Accumulation of mutations leading to cancer cells, lab could be contaminated with viruses, no guarantee of the success of treatment

Ethical issues with using stem cells

A source of embryonic stem cell is unused embryos produced by in vitro fertilisation

Social issues with using stem cells

Expensive, much of the research is being carried out by commercial clinics, patients could be exploited

Cerebral cortex

Front of the brain, used for senses, language, memory, behaviour, consciousness

Cerebellum

Back of the brain, controls balance, posture + fine muscle movement

Medulla oblongata

At the spinal cord, controls heart and breathing rate, responsible for reflexes

CT Scan

Use x-rays, no tracer injected, absorb radiation, provides structural information, indirect functional information

PET Scan

Use gamma rays, tracer injected, emit radiation, provides structural information, direct functional information

SRSCMER

She Roasted Someone Cooking Mashed Epic Roaches

Stimulus

The factor that causes a response

Sensory receptor cell

Changes stimulus into an electrical impulse, a group of receptors that respond to a particular stimulus form a sense organ

Sensory neurone

Transmits electrical impulse from sensory receptor to relay neurone in CNS

Central nervous system

The brain processes the information between different parts of the brain using relay neurones - an electrical impulse is generated in the brain

Motor neurone

Carries electrical impulse from relay neurone in CNS to the effector

Effector

Produces the response

Response

What your body does as a result of the stimulus

Structure and function of sensory neurone

Very long, has dendrites, dendron, cell body with nucleus, cell membrane and cytoplasm, axon, myelin sheath

Structure and function of relay neurone

Very short, has dendrites, cell body with nucleus, cell membrane and cytoplasm, axon

Structure and function of motor neurone

Very long, has dendrites, cell body with nucleus, cell membrane and cytoplasm, axon, myelin sheath, motor end plate

Synapse

A gap between the axon terminal of one neurone and the dendrite of another

Reflexes

Responses to stimuli that are automatic and extremely quick, often protect the body, bypass the conscious / information processing parts of the brain

Reflex arc

The route a reflex takes, which provides the shortest route from the receptor cell to the effector via the CNS

Sclera

Protection, muscle attachment, thick and tough

Conjunctiva

Membrane that lubricates the eye and provides protection from external irritants, clear to let light through, covers the white of the eye and the inside of the eyelids to form a complete barrier

Retina

Turns light into electrical impulses, contains many sensory receptor cells sensitive to light intensity or colour

Fovea

Part of the retina where the eye sees particularly good detail, has the highest density of cones

Choroid

Prevents the reflection of light rays inside the eyeball, contains a dark pigment that absorbs light

Optic nerve

Carries electrical impulses to the brain, contains sensory neurones that come from the receptor cells in the retina

Cornea

Changes the direction of light rays (refract) so they focus on retina, transparent so light can pass through, curved to change the direction of light rays

Lens

Varies the refraction of the light rays so they are focused better on retina, transparent so light can pass through, jelly-like so can change shape

Suspensory ligaments

Hold the lens in place, pull the lens to change its shape, inelastic to pull the lens properly

Ciliary muscles

Hold the lens in place, contract / relax to pull less / more on the suspensory ligaments, many muscle fibres all the way around the lens

Iris

Control size of pupil and amount of light entering the eye, contains radial and circular muscle fibres

How the eye works

Light rays come from object, cornea refracts light rays towards each other, lens refracts light rays towards each other a little more, light rays focus (meet) on retina, rods and cones change light to electrical impulse, sensory neurones in optic nerve transmit electrical impulse to brain

Near object

Light rays from object diverge more so need to be refracted more, ciliary muscle contracts, internal diameter narrows, suspensory ligaments looser, lens becomes thicker (rounder), light rays refracted more

Distant object

Light rays from object diverge less so need to be refracted less, ciliary muscle releases, internal diameter widens, suspensory ligaments tighter, lens becomes thinner (flatter), light rays refracted less

Short-sightedness / myopia

Lens is more curved than normal or the eyeball is too long which means the light is refracted too much and so the focal point falls in front of the retina - which means that distant objects appear blurry - can be corrected using contact lenses or glasses with a concave lens

Long-sightedness / hyperopia

Lens is less curved than normal or the eyeball is too short which means the light is not refracted enough and so the focal point falls in behind of the retina - which means that close objects appear blurry - can be corrected using contact lenses or glasses with a convex lens

Colour blindness

The cones in the retina do not work properly or are absent, genetically inherited condition but can also develop over time - no cure

Cataracts

Build up of protein causes clouding of the lens, light is dispersed throughout the eye or absorbed by the lens, rather than being sharply focused to one particular point, can lead to blindness - can be corrected by replacing the clouding lens with an artificial one