Topic 1: Homeostasis

Question 1

Define homeostasis

Answer 1

Homeostasis is the maintenance of a constant internal environment, mediated by feedback systems. It involves a stimulus-response model in which change in the condition of the external or internal environment is detected and appropriate responses occur via negative feedback

Question 2

What are examples of sensory receptors?

Answer 2

chemo, thermos, mechano, photo, noci

Question 3

What do sensory receptors do?

Answer 3

detect stimuli and can be classified by the type of stimulus

Question 4

What are the basic components of the control system?

Answer 4

Stimulus, receptor, coordinating system, appropriate effector, response, feedback

Question 5

What are effectors?

Answer 5

Effectors can either be a muscle (with a movement response) or a gland (which will secrete molecules). It receives information from the integrating centre and acts to bring about the changes needed to maintain homeostasis. One example is the kidney, which retains water if blood pressure is too low.

Question 6

Distinguish between positive and negative feedback in the stimulus-response model.

Answer 6

Positive feedback means the same response will continue, whereas negative feedback means the response is reversed/negated.

Question 7

What is metabolism?

Answer 7

metabolism describes all of the chemical reactions involved in
sustaining life and is either catabolic or anabolic

Question 8

What is catabolic vs anabolic

Answer 8

Anabolism is a metabolic process that builds molecules the body needs, whereas catabolism is a metabolic process that breaks down large molecules into smaller molecules.

Question 9

Describe thermoregulation

Answer 9

Thermoregulation is a mechanism by which mammals maintain body temperature with tightly controlled self-regulation independent of external temperatures. Temperature regulation is a type of homeostasis and a means of preserving a stable internal temperature in order to survive.

Question 10

what are tolerance limits?

Answer 10

Tolerance limits are the restricted range of conditions in which the cells of an organism can carry out their regular processes.

Question 11

explain why changes in metabolic activity alter the optimum conditions for catalytic activity of enzymes (with reference to tolerance limits).

Answer 11

Changes in metabolic activity can alter the internal environment, for example changing the temperature, pH or water level. If conditions such as pH or temperature change, this disrupts the bonds in the enzyme and they stop working. It is really important to maintain a constant internal environment so that enzymes can be kept within their tolerance limits, otherwise metabolism will be disrupted.

Question 12

identify cells that transport nerve impulses from sensory receptors to neurons
to effectors

Answer 12

sensory neurons—receive impulses and carry them from the sense organs to the spinal cord or brain.
interneurons—connect sensory and motor neurons and interpret the impulse; only in the brain and spinal cord.
motor neurons—carry impulses from the brain and spinal cord to muscles or glands.

Question 13

discriminate between a sensory neurone and a motor neurone

Answer 13

Sensory neurons detect stimuli such as heart rate and body temperature. They also carry information into the brain and spinal cord. Then, association neurons determine how to respond. Motor neurons respond to the association neurons decision by altering the action of effector cells and organs. association neurons are a part of the CNS (central )whereas sensory and motor neurons are apart of the PNS (peripheral).

Question 14

what are dendrites

Answer 14

Dendrites are appendages that are designed to receive communications from other cells.

Question 15

explain the process of the passage of a nerve impulse in terms of transmission of an action potential (conduction within neuron) and synaptic transmission (communication between neurones). Refer to neurotransmitters, receptors, synaptic cleft, vesicles

Answer 15

the conduction of a nerve impulse involves both chemical and electrical changes. All cells are polarised, meaning there is a difference in positive and negative charge on either side of the membrane. This is maintained by sodium ions being pumped out through special membrane channels against a concentration gradient (sodium pump). A vesicle is a small ‘package’ surrounded by a membrane which contains chemical - often neurotransmitters. Action potential arrives, which then fuses with the membrane of the axon terminal. Neurotransmitters are then released into the synaptic cleft ( a space between to neurons which connects the two)

Question 16

define postsynaptic and presynaptic neurones and

signal transduction.

Answer 16

The neuron transmitting the signal is called the presynaptic neuron (axon-knob), and the neuron receiving the signal is called the postsynaptic neuron (dendrite). Signal transduction is the process by which a cell responds to substances outside the cell through signaling molecules found on the surface of and inside the cell.

Question 17

What are hormones?

Answer 17

Hormones are chemical messengers that are produced by an organism to regulate the activity of cells and organs. Each hormone regulates and controls the activity of a specific structure. Hormones are most often produced in endocrine glands. These glands pass their secretions directly into the blood vessels, and relay messages to cells displaying specific receptors for each
hormone via the circulatory or lymphatic system

Question 18

recognise how a cell’s sensitivity to a specific hormone is directly related to the number of receptors it displays for that hormone (an increase in receptors
= upregulation, a decrease = downregulation)

Answer 18

The more receptors for a particular hormone that a cell displays, the more sensitive to that hormone it will be. When a cell displays more receptors in response to a hormone, this is called up-regulation, but when a cell reduces its number of receptors for a particular hormone, this is called down-regulation

Question 19

What are pheromones?

Answer 19

a hormone released as an external signal to other membranes

Question 20

describe how receptor binding activates a signal transduction mechanism and alters cellular activity (results in an increase or decrease in normal processes).

Answer 20

The hormone binds to the receptor protein, resulting in the activation of a signal transduction mechanism that ultimately leads to cell type-specific responses. Receptor binding alters cellular activity, resulting in an increase or decrease in normal body processes.

Question 21

What is thermoregulation?

Answer 21

Thermoregulation is a process that allows your body to maintain its core internal temperature. All thermoregulation mechanisms are designed to return your body to homeostasis

Question 22

what are the varying thermoregulatory mechanisms of endotherms and how they control heat exchange and metabolic activity

Answer 22

When your internal temperature changes, sensors in your central nervous system (CNS) send messages to your hypothalamus. In response, it sends signals to various organs and systems in your body. They respond with a variety of mechanisms.

structural features
- brown apidose tissue: tissue that stores large amounts of high energy lipids (cells that contain large numbers of mitochondria

Insulation: using fur or subcutaneous fat can help to reduce heatgain from the environment

behavioural responses

• kleptothermy: any form of thermoregulation by which an animal shares the metabolic thermogenesis of another animal (eg. huddling penguins)
• torpor: a short term state of decreased physiological activity with a reduced body temp, metabolic rate as a result of cold conditions

Physiological mechanisms
-Evaporative heat loss - sweating from glands cools the body

-Blood vessels supplying blood to the skin can swell or dilate - vasodilation. This causes more heat to be carried by the blood to the skin, where it can be lost to the air.

Question 23

define thermogenesis

Answer 23

the process of heat production in organisms

Question 24

In terms of osmoregulation, what are osmoregulators and osmoconformers?

Answer 24

From the point of view of osmoregulation, animals fall into two groups: those that cannot regulate their osmotic pressure at all (osmoconformers), and thosethat can do so to some degree (osmoregulators). Osmoregulators will manipulate the wateror solute levels so that the overall solute concentration is kept constant. Osmoconformers will allow their water and solute levels to become the same as the external environment (isotonic)

Question 25

Define osmoregulation

Answer 25

maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations

Question 26

Explain the various homeostatic mechanisms that maintain water balance in animals in terms of
­ structural features (excretory system)
­ behavioural responses
­ physiological mechanisms
­ homeostatic mechanisms (antidiuretic hormone (ADH) and the kidney)

Answer 26

Water content of the body is controlled by water loss from: lungs when we exhale, the skin by sweating, urine produced by kidneys. Ion content is controlled by loss of ions from: sweating and urine. Antidiuretic hormone (ADH) makes the collecting duct epithelium more permeable to water. An increase in osmolarity triggers the release of ADH, which helps to conserve water.

Question 27

How do freshwater animals achieve osmoregulation?

Answer 27

Freshwater animals constantly take in water by osmosis, and lose salts by diffusion. They maintain water balance by excreting large amounts of dilute urine. Salts lost by diffusion are replaced in foods and by uptake across the gills.

Question 28

How do marine animals achieve osmoregulation?

Answer 28

they lose water by osmosis and gain salt by diffusion and from food. They balance water loss by drinking seawater and excreting salts.

Question 29

What are the key functions of the excretory system?

Answer 29

Excretory systems regulate solute (water and ions) movement between internal fluids and the external environment
Filtration: filtering of body fluids
Reabsorption: reclaiming valuable solutes
Secretion: adding non-essential solutes and wastes from the body fluids to the filtrate
Excretion: processed filtrate containing nitrogenous wastes released from the body.

Question 30

Identify and explain the various mechanisms that maintain water balance in
plants in terms of structural features (stomata, vacuoles, cuticle) and
homeostatic mechanisms (abscisic acid);

Answer 30

The production of the hormone abscisic acid (ABA) controls the opening and closing of the stomata. An increase of this hormone will take place when the plant is running low on water, which consequentially closes the stomata preventing any further water loss. Adaptations to reduce transpirational water loss include:

• leaves with low surface area to volume ratio - reduced number of stomata
• sunken stomata
• hairs on leaf surface
• folding of leaf
• reduction in time the stomata are open

Question 31

What is transpiration?

Answer 31

the process by which plants absorb water through the roots and then give off water vapour through stomata in their leaves

Question 32

What factors effect transpiration rate?

Answer 32

light, temperature, humidity, wind

Question 33

What are xerophytes, hydrophytes,

halophytes and mesophytes?

Answer 33

A xerophyte is a plant that has adaptations to survive in an environment with little liquid water. A hydrophyte is any plant adapted to grow wholly or partly submerged in water or wet habitats. A mesophyte is a plant adapted to growing in well-watered soil. A halophyte is a plant that grows in waters of high salinity.

Question 34

What is the soma?

Answer 34

The soma is the cell body.

Question 35

What is an axon?

Answer 35

An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron’s cell body or soma

Question 36

What is the myelin sheath?

Answer 36

The myelin sheath is an insulating layer around nerves which allows electrical impulses to transmit quickly and efficiently along the nerve cells.

Question 37

What are the nodes of ranvier?

Answer 37

Nodes of ranvier are gaps between the myelin sheath where the axons are left uncovered which allows for fast electrical impulse along the axon

Question 38

What is the axon terminal?

Answer 38

Axon terminals are that part of a nerve cell that make synaptic connections with another nerve cell or with an effector cell.

Question 39

What is a synapse?

Answer 39

Synapses are the sites of contact between nerve cells. Synapses convert electrical signals into chemical information, which is conveyed between neurons at this site