biology 2

mitosis

mitosis is how cells divide (except gametes) to form two daughter cells

the new cells can be used for growth, development and repair

uncontrolled mitosis is cancer

(interphase) - everything doubles

PROPHASE - chromosomes condense

METAPHASE - chromosomes line up along the equator of the cell

ANAPHASE - chromatids are pulled to opposite poles of the cell by cell fibres

TELOPHASE - two nuclei form

(cytokinesis) - they split into two and

specialised cells and differentiation

animals - muscle, sperm, nerve, etc.

plants - root hair cells, phloem, xylem cells, etc

SPERM

the role of a sperm cell is to deliver genetic material to an egg in order to fertilise it

  • it only has half as much genetic material

  • flagellum

  • lots of mitochondria

  • digestive enzymes at the tip

DIFFERENTIATION

→ the process by which a stem

cell changes to become specialised

brain

regions of the brain:

  • cerebral cortex → consciousness, memory, language

    • made up of two hemispheres

  • cerebellum → balance and coordination

  • hypothalamus → regulating body temp.

  • brain stem → connects brain to spinal chord

  • medulla → control our unconscious activities like breathing

scientists study the brain by:

  • studying people who have brain damage

  • electrically stimulate different parts of the brain

  • scanning the brain (CT, X-RAYS, PET, MRI)

    • MRI and PET scans are better at scanning/mapping underlying activity

treating the brain:

  • lots can go wrong: tumours, infection, mental health, trauma

  • the skull is very fragile

  • drugs can be difficult because we don’t fully understand the brain

the nervous system

the nervous system is responsible for coordinating behaviours and responding to surroundings

  • they carry electrical impulses

  • long

  • thin

a synapse is a gap between two cells

when it reaches the end of the nerve it releases chemicals called neurotransmitters

the neurotransmitters diffuse across the synapse to the next neurone

which triggers another electrical impulse on the next cell

REFLEXES

reflexes are rapid automatic responses to stimuli to decrease the change of injury

  • stimuli is detected by receptors

  • sensory neurones

  • relay neurones

  • motor neurone

  • effector, muscle or gland

  • muscle contracts to move away from the stimili

eyes

when light hit the eye it first hits the transparent cornea so light can pass through

  • cornea has no blood so oxygen has to diffuse into the cornea instead

  • it causes the light to refract

the iris is a muscle which controls the size of the pupil

  • in bright light your retina could be damaged so there is a reflex which controls the size of your pupil

  • in bright light the pupil is constricted to prevent damage

    • circular muscles contract, radial muscles relax

  • in low light the pupil is dilated to see as well as possible

    • radial muscles contract, circular muscles relax

the pupil is just a gap to allow light through to the lens

the lens also refracts light but it can change shape to control how much it refracts the light so it can always focus the light onto the retina

the retina has cone cells (sensitive to colour of light, but don’t work very well in low light) and rod cells (black and white but more sensitive to light)

fovea is a spot on the retina with only cone cells where we focus the light onto

the optic nerve takes the impulses generated by the receptor cells to the brain

TO FOCUS ON DISTANT OBJECTS

  • ciliary muscle relaxes which allows the suspensory ligaments to contract

  • pulls the lens into a less rounded shape

  • so the light is refracted less

TO FOCUS ON A NEAR OBJECT

  • ciliary muscle contracts

  • suspensory ligaments relax

  • lens becomes more rounded

  • light is refracted more

EYE PROBLEMS

  • cataracts → cloudy lens

  • colour blindness → issue with the cones on the retina

  • longsightedness → lens can’t refract light enough or because the eyeball is too short → convex lens

  • short-sightedness → lens bends light too much or eyeball too long → concave lens

stem cells

stem cells divide by mitosis

stem cells can differentiate into specialised cells

zygote → divides lots to form an embryo with embryonic stem cells because we need lots of types of cells in our body

in an adult we have stem cells in bone marrow but they can differentiate into types of blood cells to replace damaged cells

in plants they are found in the meristem tissue (growing areas of the plant)

  • as the plant grows the cells differentiate into all the cells that the plant needs

some conditions are caused by faulty cells, e.g. type one diabetes and paralysis

  • we can use stem cells to replace the faulty cells

  • usually scientists would extract embryonic stem cells and then grow them in a lab before stimulating them to differentiate in the desired way

CONS

  • requires embryonic cells but there is a limited supply

  • rejection

  • virus transmission

  • tumour development because stem cells divide very quickly naturally

  • some people think using the embryos is wrong because they are alive

we can’t use adult stem cells in the same way because they can only differentiate into a few things however they could be used to treat blood conditions