Topic 5-Homeostasis and Response

What is homeostasis?

The regulation of internal conditions to maintain optimum conditions for enzyme action and cell function.

Name three conditions controlled by homeostasis in humans.

Body temperature, blood glucose concentration, and water content.

What is a receptor?

A cell or group of cells that detect stimuli (changes in the environment).

What is a coordinator in the nervous system?

The central nervous system (brain and spinal cord) which processes information from receptors.

What is an effector?

A muscle or gland that brings about a response.

What is a reflex action?

A rapid, automatic response to a stimulus that does not require conscious thought.

Give the reflex arc pathway in order.

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

Why are reflex actions important?

They protect the body from harm by allowing rapid responses to dangerous stimuli.

What is reaction time?

The time taken to respond to a stimulus.

Name two factors that can affect reaction time.

Age, caffeine, alcohol, drugs, and distractions.

What is the central nervous system (CNS)?

The brain and spinal cord.

What is the function of the cerebral cortex?

Controls consciousness, intelligence, memory, and language.

What is the function of the cerebellum?

Controls balance, coordination, and movement.

What is the function of the medulla?

Controls unconscious activities such as heart rate and breathing.

Why is studying the brain difficult?

It is complex, easily damaged, and difficult to access ethically.

What are hormones?

Chemical messengers released by endocrine glands and transported in the blood to target organs.

What is the endocrine system?

A system of glands that produce and release hormones.

Which gland is known as the 'master gland'?

The pituitary gland.

What hormone controls metabolic rate?

Thyroxine.

Which gland produces adrenaline?

The adrenal glands.

What is negative feedback?

A process that restores normal levels when conditions change from the optimum.

Which organ monitors blood glucose concentration?

The pancreas.

What hormone lowers blood glucose concentration?

Insulin.

What hormone increases blood glucose concentration?

Glucagon.

What causes Type 1 diabetes?

The pancreas produces little or no insulin.

How can Type 1 diabetes be treated?

Insulin injections and careful monitoring of diet.

How can Type 2 diabetes be controlled?

Carbohydrate-controlled diet, exercise, and sometimes medication.

What is ADH?

Antidiuretic hormone that controls water balance.

Where is ADH released from?

The pituitary gland.

How do kidneys respond when the body is dehydrated?

More ADH is released so more water is reabsorbed into the blood.

How does the body reduce temperature when too hot?

Sweating and vasodilation.

How does the body conserve heat when cold?

Shivering and vasoconstriction.

Name the four hormones involved in the menstrual cycle.

FSH, LH, oestrogen, progesterone.

What does FSH do?

Causes egg maturation in the ovary and stimulates oestrogen production.

What does LH do?

Triggers ovulation.

What does oestrogen do?

Builds up the uterus lining and inhibits FSH.

What does progesterone do?

Maintains the uterus lining and inhibits FSH and LH.

What is IVF?

In vitro fertilisation where eggs are fertilised outside the body and implanted into the uterus.

What is a tropism?

A directional growth response of a plant to a stimulus.

What is phototropism?

A plant response to light.

What is gravitropism?

A plant response to gravity.

What hormone controls phototropism?

Auxin.

How does auxin cause a shoot to bend toward light?

Auxin accumulates on the shaded side causing cells to elongate more, bending the shoot toward light.

Name one use of gibberellins in agriculture.

Stimulating seed germination or increasing fruit size.

What is ethene used for in plants?

Controlling fruit ripening.

In a reflex arc, in which direction does a sensory neurone carry an impulse?

From the receptor to the central nervous system (CNS).

In a reflex arc, in which direction does a motor neurone carry an impulse?

From the CNS to the effector (muscle or gland).

What happens at a synapse?

The electrical impulse triggers release of neurotransmitters which diffuse across the synaptic gap and bind to receptors on the next neurone.

Why do synapses slow down reflex responses slightly?

Because neurotransmitters must diffuse across the synaptic cleft, which takes time.

How is information transmitted along a neurone?

As an electrical impulse along the cell membrane.

Give two differences between the nervous and hormonal systems.

Nervous responses are fast, short-lived, and use electrical impulses; hormonal responses are slower, longer-lasting, and use chemical messengers in the blood.

Why are hormonal responses generally slower than nervous responses?

Hormones must be transported in the bloodstream to reach their target organs.

What is accommodation in the eye?

The process by which the lens changes shape to focus light on the retina.

How does the eye focus on a near object?

Ciliary muscles contract, suspensory ligaments slacken, and the lens becomes thicker and more convex.

How does the eye focus on a distant object?

Ciliary muscles relax, suspensory ligaments tighten, and the lens becomes thinner and less convex.

Where are light receptors located in the eye?

In the retina.

What are the two types of light receptor cells in the retina?

Rods (sensitive in low light) and cones (detect colour).

What is myopia and how is it corrected?

Short-sightedness where distant objects are blurry; corrected using a concave (diverging) lens.

What is hyperopia and how is it corrected?

Long-sightedness where near objects are blurry; corrected using a convex (converging) lens.

Explain the negative feedback response when blood glucose concentration rises.

The pancreas detects high blood glucose and releases insulin; insulin causes glucose to move into cells and stimulates the liver to convert glucose into glycogen, lowering blood glucose to normal.

Explain the negative feedback response when blood glucose concentration falls.

The pancreas releases glucagon; glucagon causes glycogen in the liver to be converted into glucose and released into the blood, raising blood glucose to normal.

What is glycogen?

An insoluble storage form of glucose stored in the liver and muscles.

Why must blood glucose concentration be controlled?

Because cells require a constant supply of glucose for respiration and large changes can damage cells.

Where is urea produced?

In the liver from the breakdown of excess amino acids (deamination).

Why are excess amino acids deaminated?

Because amino acids cannot be stored in the body.

What happens to urea after it is produced?

It is transported in the blood to the kidneys for excretion.

What is selective reabsorption in the kidney?

The process by which useful substances such as glucose, ions, and water are reabsorbed from the filtrate back into the blood.

What substances are found in urine?

Urea, excess water, and excess ions.

How does ADH affect kidney tubules?

It increases the permeability of kidney tubules so more water is reabsorbed into the blood.

How is ADH release controlled?

By negative feedback based on the water concentration of the blood detected by the brain.

How does sweating reduce body temperature?

Evaporation of sweat from the skin surface transfers energy away from the body.

How does vasodilation reduce body temperature?

Arterioles near the skin surface widen, increasing blood flow and heat loss.

How does vasoconstriction conserve heat?

Arterioles narrow, reducing blood flow near the skin surface and reducing heat loss.

How does shivering increase body temperature?

Rapid muscle contractions increase respiration, releasing more energy as heat.

How does oestrogen control FSH during the menstrual cycle?

Rising oestrogen inhibits FSH release to prevent multiple eggs maturing.

How do oestrogen and progesterone prevent pregnancy in hormonal contraception?

They inhibit FSH and LH so no egg matures and ovulation does not occur.

What is the role of LH in ovulation?

A surge in LH triggers the release of an egg from the ovary.

How does auxin distribution differ in shoots exposed to light?

Auxin accumulates on the shaded side of the shoot.

Why does a shoot bend toward light?

Auxin stimulates cell elongation on the shaded side, causing the shoot to curve toward the light.

Why do roots grow downward in gravitropism?

Auxin accumulates on the lower side and inhibits cell elongation in roots, causing the root to bend downward.

Give two agricultural uses of auxins.

Rooting powders and selective weedkillers.

Give two roles of gibberellins.

Stimulate seed germination and increase fruit size.

How are gibberellins used commercially?

To end seed dormancy and promote uniform germination.

What is ethene and how is it used commercially?

A plant hormone that controls fruit ripening and is used to ripen fruit during storage and transport.

Why is coordination necessary in multicellular organisms?

Because different organs and systems must work together to maintain stable internal conditions.

What is the word equation for aerobic respiration?

Glucose + oxygen → carbon dioxide + water (+ energy)

What is the symbol equation for aerobic respiration?

C6H12O6 + 6O2 → 6CO2 + 6H2O (+ energy)

What is the word equation for anaerobic respiration in humans?

Glucose → lactic acid (+ energy)

What is the word equation for anaerobic respiration in plants and yeast?

Glucose → ethanol + carbon dioxide (+ energy)

Function of the Cerebral Cortex, Cerebellum, and Medulla

Cerebral Cortex: Responsible for consciousness, intelligence, memory, and language, Cerebellum: Responsible for muscle coordination and balance, Medulla: Responsible for unconscious activities like heartbeat and breathing.

Process of Accommodation for Near Objects

Ciliary muscles contract, Suspensory ligaments loosen, The lens becomes thicker and more curved (more refractory), This refracts light rays more strongly to focus them on the retina.

Process of Accommodation for Distant Objects

Ciliary muscles relax, Suspensory ligaments pull tight, The lens becomes thinner and flatter (less refractory), This refracts light rays only slightly to focus them on the retina.

Negative Feedback Loop for Blood Glucose (High)

Pancreas detects high blood glucose and secretes insulin, Insulin causes glucose to move from the blood into the cells, In liver and muscle cells excess glucose is converted to glycogen for storage.

Negative Feedback Loop for Blood Glucose (Low)

Pancreas detects low blood glucose and secretes glucagon, Glucagon causes the liver to convert stored glycogen back into glucose, The glucose is released into the blood to return levels to normal.

Type 1 vs Type 2 Diabetes

Type 1: Pancreas fails to produce sufficient insulin and is treated with insulin injections, Type 2: Body cells no longer respond to insulin produced by the pancreas and is treated with a carbohydrate-controlled diet and exercise.

Role of ADH in Water Balance (Osmoregulation)

If blood is too concentrated the pituitary gland releases more ADH, ADH makes the kidney tubules more permeable so more water is reabsorbed into the blood, This results in a small volume of concentrated urine.

The Function of Dialysis

Blood is filtered externally through a partially permeable membrane, Dialysis fluid contains the same concentration of glucose and ions as healthy blood so no net movement of these occurs, Urea diffuses out of the blood into the dialysis fluid down a concentration gradient.

Comparison of Dialysis and Kidney Transplant

Dialysis: Available immediately but requires frequent long sessions and diet control, Transplant: Provides a permanent solution and better quality of life but carries risks of surgery and organ rejection and requires lifelong immunosuppressant drugs.

The Menstrual Cycle Hormones (FSH, LH, Oestrogen, Progesterone)

FSH: Matures the egg and stimulates oestrogen production, Oestrogen: Thickens uterus lining and stimulates LH while inhibiting FSH, LH: Stimulates ovulation (release of the egg), Progesterone: Maintains uterus lining and inhibits both FSH and LH.

How Oral Contraceptives and IUDs Work

Oral Contraceptives: Contain hormones to inhibit FSH so no eggs mature, IUD: Prevents the implantation of an embryo or releases hormones to thicken cervical mucus and prevent sperm reaching the egg.