AQA Biology A-level Topic 3: Organisms exchange substances with their environment Notes

Flashcards on Organisms and their Environment

Exchange

The need for specialised exchange surfaces arises as the size of the organism, and its surface area to volume ratio increases.

Efficient Exchange Surface

Efficient exchange surface should be thin to ensure that the distance that needs to be crossed by the substance is short.

Counter Current

Blood and water flow across the lamellae in a counter current direction meaning they flow in the opposite direction to one another.

Spiracles

Small openings of tubes, either bigger trachea or smaller tracheoles, which run into the body of an insect and supply it with the required gases.

Stomata

Small holes in plant leaves which allow gases to enter and exit the leaves.

Alveoli

Tiny sacs filled with air where gaseous exchange takes place in the lungs.

Cartilage

Involved in supporting the trachea and bronchi, plays an important role in preventing the lungs from collapsing in the event of pressure drop during exhalation.

Ciliated epithelium

Present in bronchi, bronchioles and trachea, involved in moving mucus along to prevent lung infection by moving it towards the throat where it can be swallowed.

Goblet cells

Cells present in the trachea, bronchi and bronchioles involved in mucus secretion to trap bacteria and dust to reduce the risk of infection with the help of lysozymes which digest bacteria.

Smooth muscle

Their ability to contract enables them to play a role in constricting the airway, thus controlling its diameter as a result and thus controlling the flow of air to and from the alveoli.

Elastic fibres

Stretch when we exhale and recoil when we inhale thus controlling the flow of air.

Ventilation

The flow of air in and out of the alveoli.

Vital capacity

The maximum volume of air that can be inhaled or exhaled in a single breath. Varies depending on gender, age, size as well as height.

Tidal volume

The volume of air we breathe in and out at each breath at rest

Digestion

The hydrolysis of large biological molecules into smaller molecules which can be absorbed across cell membranes.

Lipases

Enzymes which hydrolyse the ester bond between the monoglycerides and fatty acid.

Peptidases

Enzymes that digest proteins.

Endopeptidases

Hydrolyse peptide bonds between specific amino acids in the middle of a polypeptide.

Exopeptidases

Hydrolyse bonds at ends of a polypeptides.

Dipeptidases

Break dipeptides into individual amino acids.

Haemoglobin

A water soluble globular protein which consists of two beta polypeptide chains and two alpha helices.

Partial pressure of oxygen

A measure of oxygen concentration.

Bohr effect

In the presence of carbon dioxide, the affinity of haemoglobin for oxygen decreases, thus causing it to be released.

Blood

It is water based so substances can easily dissolve into it.

Valves

Valves are used in veins to prevent any backflow.

Aorta

Connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs.

Pulmonary Artery

Connected to the right ventricle and carries deoxygenated blood to the lungs where it is oxygenated and the carbon dioxide is removed.

Pulmonary Vein

Connected to the left atrium and brings oxygenated blood back from the lungs.

Vena Cava

Connected to the right atrium and brings deoxygenated blood back from the tissues except the lungs.

Sinoatrial node

In the wall of the right atrium there is a region of specialised fibres which is the pacemaker of the heart.

Arteries

Arteries are thick walled to withstand high blood pressure and contain elastic tissue which allows them to stretch and recoil thus smoothing blood flow.

Capillaries

Smallest blood vessels, site of metabolic exchange, only one cell thick for fast exchange of substances.

Veins

Carry blood from the body to the heart, contain a wide lumen to maximise the volume of blood carried to the heart.

Hydrostatic pressure

Hydrostatic pressure is created when blood is pumped along the arteries, into arterioles and then capillaries.

Mass transport in plants

Plants transport system to ensure that all the cells of a plant receive a sufficient amount of nutrients.

Xylem tissue

Enables water as well as dissolved minerals to travel up the plant in the passive process of transpiration.

Phloem tissue

Enables sugars to reach all parts of the plant in the active process of translocation.

Transpiration

The process where plants absorb water through the roots, which then moves up through the plant and is released into the atmosphere as water vapour through pores in the leaves.

Xerophytes

Plants adapted to living in dry conditions.

Plasmodesmata

The channels which connect the cytoplasm of one cell to the next.

Apoplast pathway

The water moves through the water filled spaces between cellulose molecules in the cell walls.

Phloem vessels

Tubes made of living cells involved in translocation of nutrients to storage organs and growing parts of the plant.

Plasmodesmata

Gaps between cell walls which allow communication and flow of substances such as minerals between the cells.

Translocation

An energy requiring process which serves as a means of transporting assimilates such as sucrose in the phloem between sources which release sucrose such as leaves and sinks e.g. roots and meristem which remove sucrose from the phloem.

Ringing experiment

Plant tissues above the missing ring swell with sucrose solution and the tissue below dies, showing that sucrose is transported in the phloem.

Tracer experiments

Plants are grown in a environment that contains radioactivity labelled carbon dioxide (14CO2) and the movement of these sugars can now be traced through the plant using autoradiography.