What is an ecosystem?

All the living organisms and non-living components in a habitat, and their interactions.

Define ‘conservation’.

Active management of an ecosystem, habitat or resource to maintain biodiversity and natural resources.

Define ‘preservation’.

Leaving ecosystems undisturbed.

What is a limiting factor?

A factor that will limit the rate of reaction when at a suboptimal level.

Define oxidation.

A reaction requiring the loss of hydrogen or loss of electron.

What is the photolysis of water?

A chemical reaction which produces protons, electrons and oxygen.

It is part of the light-dependent reaction in plants.

Define photoionisation.

Light excites electrons in the plant’s chlorophyll.

Electrons are lost and the chlorophyll becomes positively charged.

What is acetylcoenzyme A?

A molecule resulting from the combination of acetate and coenzyme A in the link reaction.

What is a calorimeter?

An instrument that can be used to determine the

chemical energy store

of a known mass of

biomass

.

Define ‘gross primary production’.

The

chemical energy store

in plant biomass, in a given

area

or volume.

Define ‘net primary production’.

The chemical energy store in plant biomass, after respiratory losses to the environment have been accounted for.

Define ‘nitrification’.

The conversion of ammonia into nitrate.

Define ‘nitrogen fixation’.

The conversion of nitrogen into ammonia.

Define ‘denitrification’.

The conversion of nitrate to nitrogen, which reduces nitrate supply.

Define ‘mutualism’.

An advantageous, nutritional relationship between two species, where both species benefit.

What is a saprobiont?

An organism that uses enzymes externally to decompose proteins, releasing ammonia.

Define ‘leaching’.

A process that removes nutrients from the soil. Soluble nutrients dissolve in rainwater and are carried deeper into the soil where plant roots cannot reach

What is a stimulus?

A stimulus is a change in the internal or external environment.

In the context of signalling, what is the structure and function of a receptor?

A receptor is a cell or protein that detects one specific type of stimulus.

In the context of signalling, what is the structure and function of the effector?

The effector is a part of the body, often a muscle or gland, that produces a response to a detected stimulus.

What are hormones?

Hormones are chemical substances, often proteins, secreted by glands and stimulate target cells via the blood system. They are specific to the tertiary structure of the receptors on target cells.

What is the nature of the duration of the response produced by hormones?

Hormones usually produce a response that is long-lasting, slow, and widespread.

In the context of signalling, what is the role of the coordinator?

The coordinator formulates a suitable response to a stimulus

Define taxis.

Taxis is the movement towards or away from a stimulus.

Define kinesis.

Kinesis is the change in speed of movement, and rate at which the organism changes direction in response to a stimulus.

What is tropism?

Tropism is the growth of part of a plant in response to a directional stimulus.

What are plant growth factors and what is their function?

Plant growth factors are chemicals which regulate plant growth in response to directional stimuli. They may move from the growing regions where they are produced to other tissues in the plant.

What is a generator potential and how is it established?

Generator potential is a nervous impulse established as a result of energy of the stimulus being transduced by a receptor.

Where are rod cells and cone cells found?

Both rod and cone cells are found in the eye.

How do rod cells in the eye work to allow high visual sensitivity?

Several rod cells are connected to a single neurone, which allows spatial summation to overcome the threshold needed to generate an action potential.

How do cone cells in the eye work to allow high visual acuity?

A single cone cell is connected to a single neurone so cones send separate impulses to the brain.

What is the function of the sinoatrial node (SAN) in the heart?

The SAN is a group of cells that sends a wave of impulses across the atria to cause atrial contraction, initiating heartbeat.

What is the structure and function of the atrioventricular node (AVN) in the heart?

The AVN is a group of cells that delays impulses so the atria can empty before the ventricles contract. The AVN sends a wave of impulses down the bundle of His and Purkyne tissue causing ventricles to contract.

Where specifically in the heart is the Purkyne tissue found?

The Purkyne tissue are specialised muscle fibres between and below the ventricles.

What is the function of the Purkyne tissue?

The Purkyne tissue conducts waves of impulses which stimulate the heartbeat.

What is the Bundle of His, and what is its function?

The Bundle of His is a structure formed by a collection of Purkyne tissues. It conducts waves of impulses which stimulate the heartbeat.

What is the function of the sympathetic nervous system?

The sympathetic nervous system stimulates effectors and speeds up activity.

What is the function of the parasympathetic nervous system?

The parasympathetic nervous system inhibits effectors and slows down activity.

How is the resting potential of neurones maintained?

The inside of an axon is negatively charged relative to the outside as a result of the distribution of sodium and potassium ions.

What is the action potential?

The change that occurs in the electrical charge across the membrane of an axon when it is stimulated and a nervous impulse passes.

What is a nerve impulse and how is specificity to a target cell determined?

A nerve impulse is a wave of electrical activity that travels along the axon membrane. It is specific to a target cell because it releases a chemical messenger directly onto the cell.

What is the nature of response produced by a nerve impulse?

Nerve impulses produce responses that are usually localised, short-lived and rapid.

What is the refractory period and what is its purpose?

The refractory period is the period after an action potential when the sodium voltage-gated channels are closed, movement of sodium ions into the axon is prevented, and so an additional action potential is prevented. It is essential to ensure discrete impulses.

Describe the all-or-nothing principle.

The all-or-nothing principle states that if the threshold value is not reached then an action potential is not generated.

What is a locus?

The position of a gene on a chromosome.

Define genotype.

The genetic constitution of an organism.

Define phenotype.

The expression of the genotype and its interaction with the environment.

What is a dominant allele?

An allele that is always expressed in the phenotype.

Define codominant.

When both alleles are expressed in the phenotype.

Define autosomal linkage.

When both alleles occur on the same chromosome so the alleles are inherited together unless crossing over occurs.

What is a species?

A group of similar organisms which can reproduce to give fertile offspring.

What is a population?

All organisms of one species in a habitat at one time.

What is the Hardy Weinberg principle?

A principle providing a mathematical model, predicting that allele frequency will stay constant over generations.

The requirements are:

 .   1. There is no mutation, selection or migration.
    2. The population is large and genetically isolated.
  3. Mating is random.

What is a selection pressure?

An environmental force altering the frequency of alleles in a population.

What is selective breeding?
Where humans breed organisms with particular characteristics.