Biology Paper 2

What is homeostasis?

The regulation of conditions to maintain an optimum internal environment in reponse to internal or external change.

What does homeostasis control?

Body temperature (37 degrees)

Blood glucose concenrtration

Water levels

Why is it important to maintain body temp, blood glucose concentration and water levels?

Its important so there’s optimum enzyme and cell function

What is homeostasis controlled by?

The nervous system and the endocrine system through this cyclical process:

Receptors in organs detect change in internal or external environment, stimulus

Information is sent via nervous impulses or hormones

Coordinates process information e.g brain, spinal cord, pancreas

Hormones or nervous impulses

Effectors are organs that respond to the stimulus, either glands or muscles

Body responds to change

What is the Central Nervous System?

Brain and spinal cord

What are the nerves that come out the spinal cord?

Bundle of nerve cells

What do nervous impulses do?

Work to allow humans to react to their surroundings and coordinate their responses.

Nerves transmit electrical impulses to send information

How are nervous impulses detected by the body to bring about a response?

(SRCER)

Stimulus is detected by receptor cells in sense organs

Nerves transmit electrical impulses to coordinator (CNS)

Coordinator to effector which is a muscle or gland that secretes hormones or contracts

Response occurs in body

Why are reflex actions important?

Unconsicous because they don’t involve the brain

Only use three neurones so known as the reflex arc

Designed to keep the body safe from harm

What examples are there of reflex actions?

Knee jerk

Pupil response to light

Coughing/ sneezing

etc

What is the reflex arc when the hand touches a sharp object?

The sharp object is the stimulus that pricks the skin

A sensory neurone sends electrical impulses to the spinal cord (the coordinator)

An electrical impulse is passed to a relay neurone in the spinal cord

A relay neurone synapses with a motor neurone

A motor neurone carries an impulse to a muscle in the hand

Muscle contracts and hand pulls away

What part of the CNS are reflex actions controlled by?

The spinal cord because an immediate response is needed and its faster than the brain

What is a synapse?

Gap between two neurones

Chemical released diffuses across and binds to receptors on next one

What is the brain?

A complex organ that controls behaviour. It is made of billions of interconnected neurones but has different ones that are responsible for different functions

What does the cerebral cortex control?

Conscious thought, language, memory, intelligence

‘higher brain functions’

What does the cerebellum control?

Coordinates muscle contractions and helps with balance and control of the body

What does the medulla control?

Unconscious behaviours like heart and breathing rate

How is the brain studied?

Studying people with brain damage/injury

Electrical stimulating brain or measuring electrical activity (EEG)

MRI scans to visualise brain structure

Why do we need to electrically stimulate the brain and use MRI’s to study it?

The brain is inside a skull which is hard to access to see how it works to treat it

Doing these procedures can help with disorders like epilepsy

What are the issues with treating the brain?

Complex (not fully understood) and delicate (easily damaged in surgery) organ

Hard to access and nervous tissue is difficult to repair or replace

Not all drugs can reach the brain due to membranes

What is the eye?

A sense organ that contains receports that can detect changes in light intensity or colour

What does the optic nerve do?

Transmits electrical impulses to the brain

What does the retina do?

Contains light receptors, rod and cone cells

What does the sclera do?

It provides support and protection

What does the iris do?

Contains muscles that control, how much light enters the eye through the pupil

What does the cornea do?

Transparent layer that protects the pupil and helps to focus light

What do the ciliary muscles and suspensory ligaments do?

Help to control the size and shape of the lens to focus light onto the retina

What are the main two roles of the eye?

Adapt to light intensity

Accommodating to focus light from near or far

How does the eye adapt to bright light?

Circular iris muscles contract

Radial iris muscles relax

Pupil is smaller so less light enters the eye

How does the eye adapt to dim light?

Circular iris muscles relax

Radial iris muscles contract

Pupil is larger so more light enters the eye

How does the eye accommodate to focus on light from nearby objects?

Ciliary muscles contract

Suspensory ligaments loosen

The lens is thicker so the light refracts more so it focuses on the retina

How does the eye accommodate to focus on light from far objects?

Ciliary muscles relax

Suspensory ligaments tighten

The lens is thinner so less light is refracted so it can focus on the retina

What are the two eye defects?

Hyperopia and myopia

What is hyperopia?

Also called long-sightedness

The lens is too flat so it cannot refract light enough and nearby objects seem blurry

How can hyperopia be fixed?

Convex lens in glasses or contact lenses to diverge the light rays

What is myopia?

Also called short-sightedness

The lens is too curved so it refracts light too much

How can myopia be fixed?

Concave lens in glasses or contact lenses which converge the light rays

What are other treatment options?

Laser eye surgery to change cornea shape

Lens replacement surgery for cataracts (cloudy lenses)

What is temperature controlled by in the body?

Thermoregulatory centre in the brain that contain receptors which detect blood temperature

Skin receptors can also tell the skin temperature and send nervous impulses to the brain if the body is too hot or too cold

What happens if the body is too cold?

Vasoconstriction - lumen of blood vessels in skin narrows to reduce blood flow

Muscle contraction/shivering - increases respiration

Hairs on skin stand up - stop sweating

Body temperature increases

What happens if the body is too hot?

Vasodilation - lumen of blood vessels widen to increase blood flow

Hars lie flat - sweating increase

Heat energy used to evaporate

What is the endorcrine system?

Made up of glands that secrete hormones directly into the bloodstream

The blood carries the hormones to target cells around the body where it has an effect

What is the differences between the endocrine system and the nervous system?

Endocrine uses chemicals not electrical impulses

Impulses transported by blood not nerves

Slower response time

Longer lasting effects

Can affect multiple organs at once

What is the pituitary gland?

Master gland - hormones released act on other glands to stimulate more hormone release

Secrets FSH and LH used in menstruation

What other endocrine glands are there?

Adrenal glands - release adrenaline

Pancreas - releases insulin and glucagon

Ovaries - release oestrogen and progesterone

Testes - release testosterone

Thyroid - thyroxine

What are blood glucose levels monitored and controlled by?

Pancreas

What happens if blood glucose is too high after a meal?

Pancreas secrets insulin - example of negative feedback because the change is reversed

What is the process that happens to decrease blood glucose levels?

Receptors in pancreas detect increase in blood glucose levels

Coordinator - pancreas secretes insulin

Insulin hormone travels in blood

Effector - insulin binds to liver cells and makes them absorb glucose from blood

Response - blood glucose levels decrease and excess glucose in liver and muscle cells are converted to glycogen

What happens if blood glucose levels are too low after exercise?

Pancreas secretes glucagon and causes cells to breakdown glycogen and release glucose into blood

What is the process that increases blood glucose levels?

Receptors in pancreas detect decrease in blood glucose levels

Coordinator - pancreas released glucagon

Glucagon hormone travels in blood

Effector - glucagon binds to liver cells and makes them release glucose into blood because the glycogen is broken down to release glucose

Response - blood glucose level increases

This with insulin forms a negative feedback cycle that keeps blood glucose levels stable around the optimum

What is diabetes caused by?

When the blood glucose levels are not being controlled properly which can cause high blood glucose levels

What is type 1 diabetes and how can it be treated?

Not enough insulin produced by pancreas

Treatment - insulin injections to help lower blood glucose

What is type 2 diabetes?

Insulin receptors do not respond to insulin anymore

Treatment - low carbohydrate controlled diet and exercise, sometimes glucose lowering medication

Risk factor - obesity

What is the importance of maintaining water levels?

Water levels in the body need to be the same as cell cytoplasm to prevent osmosis so cells don’t shrink or burst and prevent cell function

How are waste products removed from the body?

Excess water, ions and toxic substances like CO2 and urea are removed by excretion.

Water, ions and urea are lost from skin sweat - no control

Water is lost as water vapour when we exhale - no control

Excess water ions and urea are filtered by kidneys into from blood and excreted as urine from bladder - controlled by hormones

How is excess nitrogen removed?

Proteins are broken down into amino acids which contain nitrogen and cannot be stored in body

Excess amino acids are transported to live and are deaminated into ammonia and then converted to les toxic urea

What happens when kidneys filter urea from blood?

Filter urea from blood and is excreted as urine from the bladder

Blood enters and is filtered so the urea can be excreted, and the filtered blood is sent back to the heart via the renal artery to be pumped around the body

What system do the kidneys and bladder form?

The urinary system.

Its purpose is to filter the blood to remove urea, water and excess ions which leave the body in urine

How is the kidney structured for its purpose?

The kidney contains thousands of fine tubules which filter blood and then reabsorb useful substances such as glucose, some ions and water - selective reabsorption

What happens if the kidneys fail to work?

There will be a build up of toxic urea in the body

What is dialysis?

A patient is attached to a machine which removes blood from the body and filters it

Urea is removed and blood is returned to the body

Dialysis fluid flows next to the blood causing diffusion of urea and excess ions out of blood into fluid

No glucose is removed because the dialysis fluid contains glucose so all the glucose remains for respiration

Dialysis membrane between blood and fluid is semi permeable like a cell membrane

What is a kidney transplant?

From a dead or living donor that is a tissue/blood type match to reduce chances of rejection

What are the pros and cons of dialysis?

Pros - Used to keep people waiting for a kidney transplant alive

Cons - can be inconvenient to sit at the hospital for hours every few days, not long-term solution

What are the pros and cons of a kidney transplant?

Pros - long-term solution

Cons - shortage of donors and requires immunosuppressants for life

Why is water loss in urine controlled and what is this process an example of?

Controlled by hormones to make sure water levels in the body remain around the optimum

Its controlled by the pituitary gland that secrets ADH

This is an example of negative feedback

What happens if blood water levels are too high?

Receptors detect high blood water levels

Pituitary gland releases less ADH into blood

Less water reabsorbed into blood so more water removed in urine - greater volume of urine

Blood water level decreases and returns to optimum

What happens if blood water levels are too low?

Receptors detect low blood water levels

Pituitary gland releases more ADH into blood

More water reabsorbed into blood so less water removed in urine - smaller volume of urine

Blood water level increases and returns to optimum

What happens during puberty?

Human reproductive hormones are released which cause the development of secondary sex characteristics and cause physical changes that prepare the body for sexual reproduction

What hormones are released by the body during puberty?

Testes release testosterone which causes sperm production

Ovaries release oestrogen and progesterone which build and maintain uterus lining

Pituitary released FSH - egg maturing in ovary and LH - egg released from ovary

What happens during the menstrual cycle?

At day 14, the egg is released from the ovary, this is called ovulation

If the egg is fertilised, it will implant into the wall of the uterus and pregnancy occurs

If the egg is not fertilised, the egg and uterus lining will fall away from inside of uterus wall which is called menstruation

How do FSH, LH, oestrogen and progesterone interact to control the menstrual cycle?

When FSH increases, oestrogen increases so the uterus lining begins to develop, ready for egg release

When oestrogen increases it causes LH production so the egg is only released when the uterus lining is ready to receive it and inhibits FSH production so only one egg matures in a cycle

When progesterone increases, it inhibits FSH and LH production to prevent any other eggs maturing or being released during pregnancy

How do FSH and oestrogen interact?

A cycle of negative feedback

What does the decrease of progesterone towards the end of the cycle do?

It causes menstruation because the lining of the uterus is not being maintained so it breaks away and leaves through the vagina as the period

What is contraception?

Any method used to try and prevent pregnancy. It is a form of controlling fertility.

What are hormonal contraceptives?

Pill, patch and some IUD’s.

Contain progesterone and oestrogen to inhibit FSH and LH so no eggs mature or are released from the ovaries so they can’t be fertilised

What are non-hormonal contraceptives?

Condoms to stop sperm reaching egg and provide STI protection

Spermicide kills or disables sperm so they can’t swim to egg

IUD is placed in uterus to prevent an embryo implanting in the wall

Surgical sterilisation is a permanent solution to cut tubes that release gametes

How can hormones be used to treat infertility?

Fertility drugs including FSH and LH injected to increase egg maturation and release.

IVF - in vitro fertilisation - egg and sperm are collected, fertilisation in the lab in a dish, embryos formed replaced into uterus to start pregnancy

What are the pros and cons of IVF?

Pros - allows parents to have a biological child

Cons - physically and emotionally stressful, no high success rate than normal, can lead to multiple births and risk health of babies and mother, unused embryos are destroyed which is an ethical issue

What is the purpose of thyroxine?

Controls the basal metabolic rate which is important for growth and development

What happens when thyroxine is secreted?

Thyroxine is controlled by a negative feedback loop

Pituitary releases TSH (thyroid stimulating hormone) into the blood which travels to thyroid gland and caused thyroid to release thyroxine into blood.

When thyroxine is released too much, it inhibits the release of TSH so no more thyroxine is stimulated for release so thyroxine levels drop and TSH is no longer inhibited so its released again, stimulating more thyroxine. This is a continuous cycle.

What do receptors in the pituitary control with thyroxine?

Control how much thyroxine is released to change the metabolic rate

Decrease in body temp - more thyroxine released to increase metabolic rate, increases rate of respiration to release heat energy

Stress levels increase - less thyroxine is released to slow down metabolic rate, reduces the rate of respiration so more nutrients are stored as fat to help survive long term change - so having high stress levels can cause weight gain

What is the purpose of adrenaline?

Released in times of fear or stress to prepare body for ‘flight or fight’ to respond

What does adrenaline do to the body?

Reduces blood flow to digestive system

Increases heart rate

Increases breathing rate

More O2 and glucose to brain and muscles do the brain can think and react to surroundings and muscles can help us to run or fight to survive

Why is the release of adrenaline not considered a negative feedback loop?

When the danger poses, adrenaline release stops and the body returns back to normal so this is not negative feedback

Why do plants produce hormones?

To control and coordinate growth and responses to light and gravity

What is the main plant hormone?

Auxin is the hormone that controls these responses. Unequal distribution of auxin in roots and shoots causes unequal growth

What happens in phototropism?

Positive in shoots and shoots bend towards light. More auxin on shaded side causes increased cell growth

Negative in roots so they end away from the light. More auxin on shaded side inhibits growth or cell elongation

What happens in gravitropism?

Negative in shoots and they grow against the pull of gravity so there’s more chance of finding light. Auxin moves to lower side causing more cell elongation so shoot bends upwards.

Positive in roots and they grow with the pull of gravity so they grow into soil for support and to find water. Auxin moves to lower side inhibiting cell elongation so upper side grows more, bending root downwards.

What are the uses of plant hormones?

Auxins can be used as weed killers because they cause plants to grow too fast and collapse. Rooting powders for cuttings. Promote growth in tissue culture.

Ethene in plants to control cell division and fruit ripening. Humans use it in the food industry to control ripening to reduce damage from transport and storage

Gibberellins initiate seed germination and can be used to end seed dormancy, promote flowering and increase fruit size

What is sexual reproduction?

The fusion of male and female gametes produced by meiosis.

Egg and sperm in humans

Egg and pollen in plants (pollen is produced in anthers)

What does the fusion in sexual reproduction cause?

Mixes different DNA from each parent, creating variation in their offspring.

Gametes are non-identical and the fusion of each pair is random

What happens in asexual production and what organisms do it?

All bacteria, some plants and few animals do this

No gametes, only one parent cell

No mixing of DNA so no variation in offspring

Relies on mitosis to produce genetically identical clones of the parent

What is meiosis and where does it occur?

The type of cell division that produces gametes or sex cells, it occurs in reproductive organs e.g testes or ovaries

What happens in meiosis?

Normal body cell (diploid)

DNA doubles to prepare for cell division so there’s double the original chromosomes

1st Cell division so now each cell has the original amount of chromosomes

2nd cell devision produces 4 non-identical cells with half the number of chromosomes of the original parent cell (haploid) - they’re non-identical because the DNA is shuffled during meiosis

What are the differences between meiosis and mitosis?

In meiosis there are 2 cell divisions and mitosis only have 1

At the end of meiosis 4 haploid, non-identical cells are produced not two identical ones like mitosis

Why is meiosis important to produce gametes?

An egg cell with 23 chromosomes and sperm cell with 23 chromosomes fertilise, so the nuclei of each gamete fuses to form a diploid zygote with 46 chromosomes.

The zygote divides by mitosis to form identical clones of itself to form an embryo, a ball of stem cells, which also goes through mitosis and differentiation to create the different kinds of cells needed to make a foetus. Cells will continue to divide and grow the foetus and differentiation produces all of the specialised spells.

Why is mitosis important to produce gametes?

It allows the single cell number to multiple and increase the cell number to grow the foetus and form specialised cells and tissues for the foetus

How do plants reproduce sexually and asexually?

Sexually - using flowers to make seeds

Asexually - runners and bulbs

How do protists reproduce sexually and asexually?

Sexually - in the mosquito vector

Asexually - in human liver and blood cells

How do fungi reproduce sexually and asexually?

Sexually - create genetic variation

Asexually - budding off spores e.g rose black spot