Edexcel IGCSE Biology Topic 2: Co-ordination and Response

What are stimuli?

Changes in the internal or external environment that organisms detect and respond to.

What is a response in biological terms?

A change in an organism's behaviour or physiology caused by a stimulus.

What are the three essential components of a co-ordinated response?

Stimulus, receptor, and effector.

What role does the receptor play in a co-ordinated response?

It detects the stimulus and initiates a signal.

What is an effector?

A muscle or gland that produces the response to a stimulus.

What is homeostasis?

The maintenance of a constant internal environment despite changes in the external environment.

Why is homeostasis essential for organisms?

Because enzymes and cells function best under particular conditions.

What is negative feedback in the context of homeostasis?

A mechanism that reverses a change when a condition moves away from its normal level.

What is phototropism?

A plant's growth response to light.

What is geotropism?

A plant's growth response to gravity.

What is auxin?

A plant hormone that controls growth by affecting cell elongation.

How does auxin affect shoot phototropism?

It redistributes to the shaded side, causing those cells to elongate more rapidly, bending the shoot towards light.

What are the two major communication systems in humans?

The nervous system and the endocrine (hormonal) system.

How does the nervous system communicate?

Using electrical impulses transmitted along neurones.

What is the sequence of a nervous response?

Stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response.

What is the role of hormones in the endocrine system?

They act as chemical messengers produced by endocrine glands and are transported in the bloodstream.

What is the difference in speed between the nervous and hormonal systems?

The nervous system is very rapid, while the hormonal system is usually slower.

What is the central nervous system (CNS) composed of?

The brain and spinal cord.

What is the biological advantage of positive phototropism in shoots?

It allows shoots to grow towards light for photosynthesis.

What is the biological advantage of positive geotropism in roots?

It allows roots to grow downwards for anchorage and access to water and mineral ions.

What is the biological advantage of negative geotropism in shoots?

It allows shoots to grow upwards, away from gravity.

What is the biological advantage of negative phototropism in roots?

It encourages roots to grow away from light and into the soil.

What happens when light comes from one side of a plant shoot?

Auxin redistributes to the shaded side, causing that side to elongate more rapidly.

What is the role of the CNS in reflex actions?

It processes information and coordinates responses, although some reflexes are coordinated through the spinal cord.

What is the function of the endocrine system?

To regulate bodily functions through hormones that affect target cells.

How do hormones affect target cells?

They only affect cells that possess the appropriate receptors.

What is the effect of insulin on blood glucose levels?

It helps regulate blood glucose concentration.

What does the central nervous system (CNS) consist of?

The brain and spinal cord.

What is the primary function of the brain?

Processes information from receptors, coordinates responses, and controls voluntary and involuntary activities.

What role does the spinal cord play in the CNS?

Carries nerve impulses between the brain and the rest of the body and coordinates reflex actions.

What are neurones?

Specialised cells adapted to transmit electrical impulses.

What is the function of a sensory neurone?

Carries electrical impulses from receptors towards the CNS.

What is the role of a relay neurone?

Found in the CNS; passes impulses between sensory and motor neurones.

What does a motor neurone do?

Carries electrical impulses from the CNS to an effector.

What is the function of the axon in a neurone?

Carries electrical impulses along the neurone.

What is the role of dendrites in neurones?

Receive signals from other cells.

What is the purpose of the myelin sheath?

Insulates the axon and increases the speed of impulse transmission.

What are receptors?

Specialised cells that detect stimuli and initiate electrical impulses in sensory neurones.

What type of stimulus do photoreceptors detect?

Light.

Where are thermoreceptors located?

In the skin.

What is a synapse?

A small gap between two neurones or between a neurone and another target cell.

How do neurotransmitters function at a synapse?

They are released from vesicles, diffuse across the synaptic gap, and bind to receptors on the next cell.

What is a reflex action?

A rapid, automatic, and involuntary response to a stimulus.

What is the reflex arc?

The pathway that a reflex action follows, including receptors, sensory neurone, relay neurone, motor neurone, and effector.

What happens when a stimulus is detected by receptors in the skin?

An electrical impulse travels along a sensory neurone to the spinal cord.

Why are reflex actions important?

They are rapid, automatic, and reduce the risk of injury.

What is the function of the cornea in the eye?

Refracts light as it enters the eye and provides much of the eye's focusing power.

What does the iris control?

The size of the pupil.

What is the role of the lens in the eye?

Refracts light to focus it onto the retina.

What is the function of the retina?

Contains photoreceptors that convert light into electrical impulses.

What does the optic nerve do?

Carries electrical impulses from the retina to the brain.

What is the sclera?

The tough outer layer that protects the eye and maintains its shape.

What is the choroid's function in the eye?

Contains blood vessels supplying the eye and pigment that absorbs stray light.

What is the function of the choroid in the eye?

It contains blood vessels supplying the eye and pigment that absorbs stray light.

What is the blind spot in the eye?

The point where the optic nerve leaves the eye; it contains no photoreceptors.

What are the two main types of photoreceptors in the retina?

Rods and cones.

What is the primary function of rod cells?

They are sensitive to low light intensities and provide black-and-white vision.

What is the primary function of cone cells?

They work best in brighter light and provide color vision.

What is the fovea?

A small region of the retina containing a high density of cone cells, responsible for sharp central vision.

What is accommodation in the context of eye function?

The process by which the eye changes the shape of its lens to focus objects at different distances onto the retina.

What happens to the ciliary muscles when focusing on distant objects?

The ciliary muscles relax, causing the lens to become thinner and less convex.

What is the pupil reflex?

It controls the amount of light entering the eye through the contraction and relaxation of the iris muscles.

What occurs in the pupil reflex in bright light?

Circular muscles contract, radial muscles relax, and the pupil constricts.

What occurs in the pupil reflex in dim light?

Circular muscles relax, radial muscles contract, and the pupil dilates.

What is thermoregulation?

The control of body temperature.

What is the normal internal body temperature in humans?

Approximately 37°C.

What happens when the body is too hot?

Sweating increases, and vasodilation occurs, allowing more blood to flow to the skin surface.

What is vasoconstriction?

The constriction of arterioles supplying the skin, reducing blood flow and heat loss when the body is too cold.

What is the role of insulin in the body?

It lowers blood glucose concentration when it becomes too high.

What are the effects of adrenaline on the body?

Increases heart rate, breathing rate, and blood glucose concentration, and redirects blood flow to muscles.

What triggers the release of insulin?

An increase in blood glucose concentration.

What is the response of the body when it is too cold?

Vasoconstriction occurs, shivering increases, and sweating decreases.

What is the net effect of responses when the body is too hot?

More heat is lost from the body.

What is the net effect of responses when the body is too cold?

Less heat is lost and more heat is produced.

What is the main function of insulin?

Stimulates the liver and muscles to convert glucose into glycogen for storage and helps lower blood glucose concentration.

What is the source of testosterone?

Mainly produced in the testes.

What are the effects of testosterone during puberty?

Growth of facial and body hair, deepening of the voice, increased muscle development, and maintenance of male reproductive organs.

What is the primary role of oestrogen?

Promotes female secondary sexual characteristics and regulates the menstrual cycle.

What effects does oestrogen have on the female body?

Development of breasts, widening of hips, stimulation of uterine lining repair, and regulation of FSH and LH release.

What is the main source of progesterone?

Mainly produced by the corpus luteum in the ovary after ovulation and by the placenta during pregnancy.

What is the role of progesterone in pregnancy?

Maintains the uterine lining and supports pregnancy.

How does ADH function in the body?

Regulates the amount of water reabsorbed by the kidneys, helping maintain body water content.

What happens when the body has too little water?

ADH is released, increasing kidney collecting ducts' permeability to water, leading to more water reabsorption and concentrated urine.

What is the source of FSH?

Produced by the anterior pituitary gland.

What is the role of FSH in females?

Stimulates the maturation of a follicle containing an egg and stimulates oestrogen secretion.

What is the role of LH in females?

Triggers ovulation and stimulates the formation of the corpus luteum.

What is the role of LH in males?

Stimulates the Leydig cells in the testes to produce testosterone.

What hormone is responsible for the fight-or-flight response?

Adrenaline.

What is the main role of insulin?

Lowers blood glucose levels.

What hormone regulates the menstrual cycle?

Oestrogen.

What hormone maintains the uterine lining after ovulation?

Progesterone.

What is the main effect of FSH in males?

Stimulates sperm production in the testes.

How does the body respond when there is too much water?

Less ADH is released, leading to less water reabsorption and more dilute urine.

What is the relationship between FSH and oestrogen in the menstrual cycle?

FSH stimulates an ovarian follicle to mature, which produces oestrogen that helps rebuild the uterine lining.

What hormone inhibits the release of FSH and LH during pregnancy?

Progesterone.

What is the function of the corpus luteum?

Secretes progesterone to maintain the uterine lining.

What is the role of the hypothalamus in ADH production?

The hypothalamus produces ADH, which is stored and released by the posterior pituitary gland.

What is the effect of high oestrogen levels on LH?

High oestrogen levels trigger a surge in LH, leading to ovulation.

What hormone is produced by the adrenal glands?

Adrenaline.

What hormone is primarily responsible for sperm production?

FSH in males.