Homeostasis

What stimuli do plants respond to?

• light (photo)

• water (hydro)

• gravity (geo)

Tropism meaning

Tropism is the turning of all or part of an organism in a particular direction in response to an external stimulus.

Phototropism meaning

A response to light

Positive phototropism:

Shoots bend towards light

Negative phototropism:

Roots bend away from light

Geotropism meaning

A response to gravity

Negative geotropism:

Shoots grow against force of gravity

Positive geotropism:

Roots grow in direction of force of gravity

3 Plant Hormones

• Auxins: Promote growth in shoots, stop growth in roots

• Gibberellins: Control cell devision

• Ethene: Regulates development and initiates germination 

auxins & phototropism

auxins are mostly made in the tips of the growing stems and roots

Unequal distribution of auxin can cause unequal growth rates in plants and shoots. Auxins change the rates of elongation in plant cells and control growth of stems and roots.

Stems and roots respond differently to high concentrations of auxins:

• cells in stems grow more

• cells in roots grow less

In a stem, the shaded side contains more auxin and causes cell elongation, which causes the stem to grow towards the light. The plant does NOT bend towards the light. It grows because the auxin causes the cells to elongate on the shaded side, so this side grows more. This unequal growth of the two sides, results in the growth of the stem towards the light.

If lit from above, the plant will grow upwards.

Auxins – Roots - Gravity

auxins: function & agricultural use

gibberellins: function & agricultural use

Regulates developmental processes including seed germination 

• Ends seed dormancy

• Promotes flowering

• Increases fruit size

ethene: function & agricultural use

Controls cell division

• Controls fruit ripening

identify the tropism:

• an upright shoot grows & bends towards light from one side

• a horizontal underground root grows & it bends down

• a root grows and bends away from light

1. positive phototropism

2. positive gravitropism

3. negative phototropism

plant hormones are used in weedkillers so…

…so that only plants with broad leaves are destroyed (not those with narrow leaves)

plant hormone meaning

a natural chemical messenger that controls how a plant grows, develops, and responds to its environment

Explain two reasons why a germinated root will grow downwards

A germinated root grows downwards because of positive gravitropism (also called geotropism), which is controlled by the plant hormone auxin

• Gravity pulls auxin: Gravity causes auxin to accumulate on the lower side (underside) of a root.

• Auxin inhibits growth: Unlike in shoots where auxin promotes cell elongation, high concentrations of auxin in the root inhibit cell growth and elongation.

• Unequal growth rates: Because the lower side has more auxin and grows slower, the cells on the upper side of the root elongate and grow faster.

• Bending downwards: This difference in growth rate causes the root to bend and grow downward in the direction of gravity

what effect do auxins have on the cells in shoot tips and why is this advantageous?

They cause elongation and the plant shoots will grow towards the light. This will then increase the amount of sunlight the plant gets for photosynthesis.

describe how different factors from the environment can affect:

• the direction of shoot growth

• the direction of root growth

The response of a plant to an environmental stimulus is called tropism. Common stimuli to plants include light, gravity and water. A shoot grow upwards towards the light, this  is called phototropism. Shoots grow away from the force of gravity (negative geotropism).  When a root grows downwards in the direction of the force of gravity, this positive geotropism. Roots will also grow towards moisture (positive hydrotropism). 

Plant hormones can be used to control the growth of plants and crops. Auxins change the rate of elongation in plant cells, controlling their length. Unequal distribution of hormone causes unequal growth rates. Higher concentrations of auxins causes faster growth in shoots. Higher concentrations of auxins cause cells in the roots to grow less. 

explain how the trophic responses are important to help plants survive

Positive tropisms make sure the plants grow towards light and water. Phototropism allows the leaves of the plant to absorb light so they can photosynthesise and produce more glucose. Positive tropism also allows plants to grow towards sources of water. 

Germination meaning

the start of growth in seeds

factors which affect successful seed germination

water, warmth and oxygen concentration

why most seeds germinate during Spring

soil temperatures are higher

Gibberellins use for farmers & seeds

Gibberellins are the hormone which cause a seed to break dormancy. Farmers can use spray gibberellins onto newly sown crops to trigger seeds to germinate out of season. This is useful to meet the demands of growing crops and providing out of season fruit and vegetables. It also ensures that all seeds germinate. Farmers can then grow plants in grow houses and provide the perfect amount of water and warmth to ensure germination.

Give two reasons why it is useful for a young root to grow towards gravity.

• anchorage

• takes in water

• takes in ions / minerals / salts

• use a piece(s) of thread / string and measure length of thread (with

  ruler)

• straighten seedling / shoot and measure (with ruler)

(d)  (side nearest the lamp) receives more light (on side P)

(therefore) unequal distribution of auxin

(auxin causes) more growth on side away from the lamp

(e)  ethene is released from bananas

Investing the effect of light or gravity on the growth of newly germinated seedlings apparatus

• Mustard seeds

• 3 Petri dishes

• Cotton wool

• A ruler

• Water

Investing the effect of light on the growth of newly germinated seedlings apparatus

1. Set up 3 petri dishes

2. Soak cotton wool in equal amounts of water

3. Put 10 mustard seeds in each dish

4. Put dishes in a warm place.

5. Allow mustard seeds to germinate (water daily with equal amounts of water to each dish)

6. Each dish should have the same number of seeds germinated. Remove any excess seeds.

7. Measure the height of each seedling in mm.

8. Move the petri dishes into position: one in full sunlight, one in partial light and one in darkness. 

9. Measure the height of each seedling every day, for at least five consecutive days. 

10. Record the heights in a table

Homeostasis meaning

Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes

stimulus meaning

A stimulus is any change in the internal or external environment e.g., a decrease or increase in the concentration of glucose in the body or touching a hot pan. 

receptor meaning

A receptor is a specialised cell which detects the change. They are found in sense organs eyes, ears, nose, skin and mouth. 

effector meaning

An effector is a muscle or a gland which bring about change in the body that will bring levels back to the optimum. 

Homeostasis maintains optimal conditions for enzyme action and all cell functions.

In the human body, these include control of:

• blood glucose concentration

• body temperature

• water levels.

coordination centres

(such as the brain, spinal cord and pancreas) that receive and process information from receptors

receptor examples

For example, rods and cones are specialised cells in your eyes that absorb light and form an image. 

Glands

Glands release hormones which create a response e.g. adrenaline which increases heart rate or ovaries releasing oestrogen.

Muscles

Muscles trigger movement of body parts and smaller changes like hairs standing on end when you get cold!

Why do we need to control conditions within the body? blood glucose & water levels

Both blood glucose concentrations and water levels can cause damage to cells all through the body due to the effect of osmosis. For example, consistently high blood glucose levels can cause damage to capillaries and lead to loss of sight. 

Why do we need to control conditions within the body? temperature

Temperature is important to control as almost all the chemical reactions in the body are controlled by enzymes.

Describe the changes in the body when blood glucose levels increase above optimum. 

Pancreas detects an increase in blood glucose levels

Pancreas releases insulin 

Insulin targets liver and muscle cells to take up glucose and convert to storage molecule

Describe how the body responds to increasing body temperature. 

1. Blood temperature is detected by receptor cells in the brain. 

2. Person starts sweating 

3. Sweating allows for cooling of skin through heat loss via evaporation. 

• Shivering/muscle contract

• vasoconstriction/constriction of blood vessels

The nervous system enables animals to…

react to their surroundings and coordinate their response.

CNS & PNS

The brain and spinal cord form the central nervous system (CNS)

The nerves that branch out form the peripheral nervous system (PNS)

How does the nervous system work?

A stimulus (light, chemical..) will be detected by a receptor (eyes, nose..) 

Electrical impulses travel along specialised cells called neurons. 

The CNS (central nervous system) will coordinate these impulses. 

An effector will cause a response to occur.

Neurons

specialised cells which carry electrical impulses through the body.

motor neuron structure

A long fibre (axon) which is insulated by a fatty (myelin) sheath. They are long so they can carry messages up and down the body.

Tiny branches (dendrons) which branch further as dendrites at each end. These receive incoming impulses from other neurones.

The nerve endings is where the nerve will meet another nerve and pass on information through something called a synapse. 

sensory neuron structure

 the cell body is in the middle of the axon in a sensory neurone. This is because these neurons are incredibly long

dendrites

tiny branches which enable the neuron to receive lots of different electrical impulses. 

These then travel through the neurone and then passed onto the correct effector.

why is myelin sheath important

Myelin sheath acts as insulator 

Without it no insulation so impulses travel more slowly. 

measure reaction times

What is a reflex action?

Reflex actions are important for protecting the body from harm

Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.

Reflex actions that involve sense organs near the brain will go through the unconscious part of the brain. All others will go through the spinal cord.

Reflex actions include:

pupils constricting in response to bright light, moving your hand in response to touching a hot object.

How does a reflex action work?

The route of a reflex action is called a ‘reflex arc’

The sensory neurone is close to your SENSES.

The relay neurone links the neurones transferring the information like in a relay race. 

The motor neurone will cause movement (motor).

synapse meaning

A synapse is a junction between two neurones. 

function of synapses

Synapses are very important in controlling the direction of a nervous impulse. 

The presence of synapses mean that the impulse only travels in one direction. 

They can also prevent the transmission of weaker stimuli and prevent the nervous system being overloaded.

pre-synaptic and post-synaptic neurons

The neuron before the synapse is called a pre-synaptic neuron.

The neuron after the synapse is called the post-synaptic neuron. 

electrical impulses

Information travels through neurons as electrical impulses. 

When the impulse reaches the synapse, it triggers the release of a chemical called a neurotransmitter. 

Neurotransmitter meaning

chemical that diffuses across a synapse and triggers a response in the post synaptic neuron.

This chemical diffuses across the synapse to the next neuron. 

This then is converted back to an electrical impulse in the next neurone.

Diffusion Direction & Rate

Neurotransmitters move across the gap purely by diffusion (passive transport) from a high concentration at the pre-synaptic end to a low concentration at the post-synaptic end.

diffusion across the gap takes time so synaptic transmission is slower than electrical transmission along an axon

Synapses slow down…

the speed of nervous transmission.

The more synapses in a reflex arc…

…the slower the speed of the nervous response.

Synapses can also be affected by…

drugs like alcohol and caffeine. 

Alcohol will slow down the transmission of the chemical neurotransmitter. Whereas caffeine will speed up the transmission of the chemical neurotransmitter.

In some cases, drugs can block the release of neurotransmitters.

Specific Receptor Sites

Neurotransmitters don't just land on the next neurone; they bind to complementary, specific receptor proteins on the membrane of the post-synaptic neurone.

How do drugs affect a synapse?

Some drugs can mimic the action of the chemical neurotransmitters or block them. 

This is because they have a similar shape to the original neurotransmitter.

it has a similar shape to the neurotransmitter and binds to the specific receptor sites.

They can bind to the receptors and change the response in the post-synaptic neurone or stop the neurotransmitter binding. 

For example, morphine is similar in shape to dopamine, our natural pain killer, and will be able to bind to the receptors instead of dopamine.

Fewer synapses found in the spinal cord 

Synapses slow down transmission so fewer of them will mean faster overall speed.

synapse vs synaptic gap

• The Synapse: The entire structure where two neurones meet, including the pre-synaptic neurone ending, the gap, and the post-synaptic neurone membrane with its receptors.

• Synaptic Gap: Strictly the microscopic space between the two neurones that the neurotransmitter diffuses across.

Destruction & Reuptake of Neurotransmitters

After the new electrical impulse is triggered in the post-synaptic neurone, the neurotransmitters are either broken down by enzymes or reabsorbed back into the pre-synaptic neurone.

This step is crucial because it resets the synapse and prevents continuous, uncontrolled firing of electrical impulses along the next neurone.

The endocrine system is made of…

glands

glands function

Glands secrete chemicals called hormones into the blood.

The blood carries the hormone to a target organ.

hormone meaning & examples

A hormone is a chemical messenger produced by a gland and carried by the blood.

• Oestrogen

• Testosterone

• Insulin

Glands of the Endocrine System

• The pituitary gland in the brain acts as the master gland

• The thyroid gland releases thyroxine that regulates basal metabolic rate

• Adrenal glands release adrenaline which increase heart rate

• The pancreas releases insulin that regulates blood glucose concentration

• The ovaries release oestrogen and the testes release testosterone which cause the development of secondary sexual characteristics during puberty

thyroxine

Thyroxine is a hormone released by the thyroid gland.

It is responsible for regulating the heartbeat and controlling your metabolism.

It is also responsible for regulating the amount of calcium in your blood.

Sometimes people have a condition called hyperthyroidism. This is when they produce too much thyroxine.

Puberty meaning

Puberty is the time in life when a child's body matures into an adults body.

Glands in the reproductive organs start to release hormones that cause the development of secondary sexual characteristics.

Oestrogen and testosterone

Oestrogen is released from the ovaries of females.

Testosterone is released from the testes of males.

Changes to females & Changes to males in puberty

The endocrine system is an … system because a gland is an organ

organ

Compare the endocrine system and the nervous system.

Both systems respond to external and internal conditions.

• Both systems send signals around the body.

• The nervous system sends signals down neurons whereas the endocrine system sends signals in the blood.

• The nervous system causes responses that are fast and short whereas the endocrine system causes responses that are slow and long lasting.

• The endocrine system sends signals via the blood whereas the nervous system sends signals via electrical impulses.

hormone, gland, target cell

label the glands