Co-ordination & Response (Edexcel IGCSE Science (Double Award): Biology): Flashcards

True.

It lets the organism escape predators, find food and keep its internal conditions within safe limits.

Stimulus ➔ receptor ➔ response

The maintenance of a constant internal environment.

It keeps optimal conditions for enzyme activity and cell function, letting the organism survive and respond to change.

If conditions go beyond set limits, the organism may die.

• Control of body temperature

• Control of body water content

Close to 37 °C.

Because the body's enzymes work best at this temperature — much above it they denature, and much below it reactions become too slow.

• Sweat is released and evaporates, taking heat energy away from the body

• Vasodilation — blood vessels near the skin surface widen, so more heat is lost

• The lungs, in breathed-out air

• The skin, in sweat

• The kidneys, in urine

The conditions inside the body that surround the cells, such as temperature and water content.

• A stimulus

• A receptor

• An effector

It carries out the response — for example a muscle contracting or a gland releasing a hormone.

A plant shoot growing towards light, or a person shivering when the air turns cold.

A stimulus is a change in the environment that a receptor detects.

When the body is too cold, blood vessels near the skin surface narrow — this is called vasoconstriction.

False.

Homeostasis is involuntary — you do not consciously maintain your body temperature or water content.

False.

Conditions fluctuate slightly around a set level — homeostasis keeps them within narrow limits, not perfectly fixed.

• A stimulus — a change in the environment

• A receptor — which detects the stimulus

• An effector — a muscle or gland that brings about the response

A muscle or gland that brings about a response to restore optimum levels.

The central nervous system — the brain and the spinal cord.

Because it is automatic — the brain and spinal cord maintain it without any conscious thought.

• Nervous responses

• Chemical responses, for example via hormones

• A change in glucose levels in the blood

• A change in body temperature

It receives and processes information from the receptors, then sends impulses out to the effectors.

An effector is a muscle or gland that brings about a response.

Impulses from receptors travel into the central nervous system, made up of the brain and spinal cord.

False.

Some are nervous responses, but others are chemical responses carried by hormones.

False.

A receptor detects the stimulus; an effector — a muscle or gland — carries out the response.

Stimulus ➔ receptor ➔ effector ➔ response

A directional growth response made by a plant to a stimulus such as light or gravity.

• Positive — growth towards the stimulus

• Negative — growth away from the stimulus

To ensure their leaves absorb light for photosynthesis, and that shoots grow upwards while roots grow downwards.

Growth towards or away from the direction of a light source.

Growth towards or away from the source of gravity. Also called gravitropism.

Positive phototropic and negative geotropic — they grow upwards, towards light, so the leaves can absorb sunlight.

Negative phototropic and positive geotropic — they grow downwards into the soil, to anchor the plant and absorb water and minerals.

A plant growth regulator, similar to an animal hormone, that co-ordinates and controls directional growth responses such as phototropism.

It is mostly made in the tips of growing shoots, then diffuses down to the region just below the tip where cell division occurs.

It stimulates them to elongate — get longer. The more auxin present, the faster they elongate and grow.

When light shines predominantly from one side, auxin made in the tip concentrates on the shaded side.

Cells on the shaded side elongate faster than those on the sunny side.

This unequal growth makes the shoot bend towards the light.

Auxin is distributed evenly, so the cells grow at the same rate and the shoot grows straight up.

In a shoot lit from one side, auxin concentrates on the shaded side.

Roots show a positive geotropic response, growing downwards towards gravity.

False.

Auxin causes the cells that already exist to elongate. It does not increase the overall number of cells.

True.

Cell division and cell elongation happen just below the tip, which is where auxin diffuses to.

• The nervous system

• The hormonal system, also called the endocrine system

As electrical impulses, which pass very quickly along nerve cells called neurones.

As chemical substances called hormones, carried in the blood so they circulate round the whole body.

A group of cells that produces and releases one or more substances — a process known as secretion.

The nervous system — for example the withdrawal reflex when a hand touches a flame.

One or more specific target organs, whose activity they alter.

• Nervous system — nerves (bundles of neurones), the brain and the spinal cord

• Endocrine system — glands

• Nervous — very fast

• Endocrine — slower

• Nervous — specific and localised, acting on particular cells

• Endocrine — widespread, affecting many cells or organs

• Nervous — short, stopping quickly

• Endocrine — long, lasting until the hormone is broken down

Hormones are transported around the body in the blood.

Electrical impulses pass along nerve cells called neurones.

False.

Nervous responses are very fast; hormonal responses are slower but last longer.

True.

Because hormones travel in the blood to the whole body, their effects are widespread.

• The brain

• The spinal cord

All of the nerves that branch out from the CNS to the rest of the body.

A bundle of neurones.

As electrical impulses — fast-moving electrical signals that pass along cells called neurones.

It acts as the central co-ordinating centre, processing incoming information from the sense organs and co-ordinating the body's response.

It produces electrical impulses, which travel along sensory neurones to the CNS.

Motor neurones, which carry impulses to the effectors — muscles or glands.

Stimulus ➔ receptor ➔ sensory neurone ➔ CNS ➔ motor neurone ➔ effector ➔ response

It carries out the response — for example a muscle contracts or a gland secretes.

• Light

• Sound

• Touch

• Temperature

• Chemicals

The central nervous system consists of the brain and the spinal cord.

Impulses travel to the CNS along sensory neurones.

False.

A neurone is a single nerve cell. A nerve is a bundle of neurones.

True.

Nerves extend from the CNS to all areas of the body, including the sense organs, allowing communication between the brain and the rest of the body.

The tiny gap between two neurones.

A chemical messenger released at a synapse that carries the signal from one neurone to the next.

The electrical impulse reaches the end of one neurone and triggers the release of neurotransmitters.

These diffuse across the synapse and bind to the next neurone.

This causes a new electrical impulse to be generated.

Because neurones are not directly connected to each other — there is a gap, so the signal cannot pass electrically.

Diffusion.

An electrical impulse arriving at the end of a neurone.

A new electrical impulse is generated, so the signal continues along the pathway.

The tiny gap between two neurones is called a synapse.

Neurotransmitters cross the synapse by diffusion and bind to the next neurone.

False.

The signal crosses chemically, carried by neurotransmitters that diffuse across the gap, before a new impulse is generated.

True.

They are released at the end of one neurone and bind to the next, passing the signal on.

No. They are separated by a synapse, a tiny gap.

An involuntary response that does not involve the conscious part of the brain as the co-ordinator.

Awareness of it comes after the response has happened.

The pathway taken by electrical impulses during a reflex action.

They are automatic and rapid, which helps minimise damage to the body and aids survival.

• Pain withdrawal

• Blinking

• Coughing

A receptor in the skin detects the stimulus.

A sensory neurone sends impulses to the spinal cord, which acts as the co-ordinator.

The impulse passes to a relay neurone in the spinal cord.

The relay neurone synapses with a motor neurone.

The motor neurone carries the impulse to a muscle (the effector), which contracts and pulls the finger away.

The spinal cord, part of the CNS — not the conscious part of the brain.

The relay neurone, in the spinal cord.

A muscle, which contracts to pull the body part away from the harmful stimulus.

Stimulus ➔ receptor ➔ sensory neurone ➔ relay neurone ➔ motor neurone ➔ effector ➔ response

In a reflex arc, the impulse passes to a relay neurone in the spinal cord.

A reflex response is also known as an involuntary response.

False.

Awareness of a reflex comes after the response has already been carried out — which is what makes it so fast.

True.

Like coughing and pain withdrawal, it is automatic and helps avoid serious injury — in this case damage to the eye.

It is a highly specialised organ containing receptor cells that allow us to detect the stimulus of light.

A clear membrane covering the white of the eye and the inside of the eyelids.

It lubricates the eye and protects it from external irritants.

A transparent, curved layer at the front of the eye that refracts light as it enters.

The strong outer wall of the eyeball. It keeps the eye in shape and provides attachment for the muscles that move the eye.

A circular opening in the centre of the iris that allows light to enter the eye.

It controls how much light enters the pupil.

A transparent disc that can change shape to focus light onto the retina.

A ring of muscle that contracts and relaxes to change the shape of the lens.

They connect the ciliary muscle to the lens.

It contains the receptor cells sensitive to light.

Cornea ➔ pupil ➔ lens ➔ retina

Impulses then leave the eye along the optic nerve.

It carries impulses between the eye and the brain.

The point where the optic nerve leaves the eye, at which there are no light receptor cells.

Light-sensitive receptor cells are found in the retina of the eye.

Light is refracted as it enters the eye by the transparent, curved cornea.

False.

They are ligaments connecting the ciliary muscle to the lens — they tighten or loosen, they do not contract.

True.

It is the point where the optic nerve leaves the eye.

The way the lens brings about the fine focusing of light onto the retina.

The lens is elastic. The ciliary muscles contract or relax, which makes the suspensory ligaments tighten or loosen and so changes the lens shape.

The ciliary muscles contract, so the ring of muscle decreases in diameter.

The suspensory ligaments loosen, so they stop pulling on the lens.

The lens becomes thicker, and light is refracted more.

The ciliary muscles relax, so the ring of muscle increases in diameter.

The suspensory ligaments tighten and pull on the lens.

The lens becomes thinner, and light is refracted less.

To protect the retina from damage by controlling how much light enters the eye.

It dilates (widens), to let as much light as possible into the eye and improve vision.

It constricts (narrows), to stop too much light entering and damaging the retina.

The pupil takes a moment to constrict.

Until it does, too much light reaches the retina.

The iris, a ring of muscle surrounding the pupil.

To focus on a near object the ciliary muscles contract and the lens becomes thicker.

In bright light the pupil constricts to protect the retina from damage.

False.

Suspensory ligaments are not muscles — they tighten or loosen. It is the ciliary muscles that contract and relax.

True.

It happens automatically, without conscious thought, to protect the retina.

A thicker (fatter) lens refracts light more, and is used when focusing on near objects.

It contains many receptors that detect external stimuli, including touch, pressure, pain, heat and cold.

When the muscles in the walls of the arterioles near the skin relax, so the arterioles widen and more blood flows through the skin capillaries.

When the muscles in the walls of the arterioles near the skin contract, so the arterioles narrow and less blood flows through the skin capillaries.

A greater volume of blood flows through the capillaries near the skin surface, so more heat is lost to the environment by radiation.

A smaller volume of blood reaches the skin capillaries, so less heat is lost by radiation.

Sweat is secreted by the sweat glands and evaporates, using heat energy from the body to convert liquid water into water vapour.

Vasodilation — arterioles supplying the skin capillaries widen, so more blood flows near the surface and heat is lost by radiation.

Sweating — sweat evaporates from the skin surface, cooling the body.

Vasoconstriction — arterioles supplying the skin capillaries narrow, reducing blood flow to the skin and so reducing heat loss.

Sweating decreases — less sweat is produced, so less heat is lost by evaporation.

It does not raise the temperature of the blood — it only reduces heat loss from blood flowing through the skin.

Sweat only cools the body when it evaporates.

In humid air the water vapour cannot escape easily, so evaporation slows and less heat is removed.

In the skin, which contains both heat receptors and cold receptors.

Because the body's enzymes work best close to 37 °C — far above it they denature, and far below it reactions become too slow.

During vasodilation the arterioles near the skin widen so more heat is lost by radiation.

Sweat cools the skin as it evaporates, using heat energy from the body.

False.

It is the arterioles that widen. That lets more blood flow through the skin capillaries.

True.

The surface is where the blood comes into closest proximity to the environment, so it is where heat is both lost and gained.

A chemical substance produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.

In the adrenal gland.

It readies the body for a 'fight or flight' response, in situations where the body may be in danger.

• Increased heart and breathing rate, delivering glucose and oxygen faster

• Blood flow redirected to the muscles, away from non-essential organs

• Dilation of blood vessels in the muscles

• Breakdown of stored glycogen to glucose in the liver and muscle cells

In the pancreas, which acts as an endocrine gland.

Its role is to lower blood glucose levels.

Cells in the pancreas detect the rise and secrete insulin into the blood.

Insulin stimulates the muscles and liver to take up glucose and store it as glycogen.

Blood glucose falls back to normal, and the pancreas stops secreting insulin.

Cells of the body can lose water by osmosis.

The brain receives insufficient glucose for respiration, which can lead to a coma or even death.

In the male testes.

It stimulates the development of the male reproductive organs and the secondary sexual characteristics in males — facial, pubic and underarm hair, deepening of the voice, and increased muscle mass.

In the female ovaries.

It maintains the uterine lining during pregnancy and prevents further ovulation.

In the female ovaries.

It causes the secondary sexual characteristics in females — breast development, wider hips, pubic and underarm hair — and helps regulate the menstrual cycle.

It stimulates the repair and thickening of the uterus lining after menstruation, preparing it to receive a fertilised egg.

• The pancreas

• The liver

Insulin causes excess blood glucose to be stored in the liver and muscles as glycogen.

Adrenaline is produced by the adrenal gland.

False.

It acts as an endocrine gland, secreting insulin into the blood, but it also has a separate digestive role, secreting enzymes into the digestive system.

True.

Blood glucose concentration must be kept within a narrow range, just like core body temperature.