Biology - EDEXCEL IGCSE - Transport

Transport:

Diffusion is heavily involved in gaseous exchange. It is the method where by most gases move.

Single, unicellular organisms can rely on diffusion for movement of substances into and out of cells. This is because they are relatively small and so can rely on diffusion compared to larger multicellular organisms, which are so large that to only rely on diffusion would mean substances will be delivered around the organism very slowly.

Because of this, multicellular organisms must also have a transport system which allows for a more efficient method of movement of substances.

Transport in plants:

Osmosis - the movement of water molecules from a high water potential to a low water potential through a semi-permeable membrane.

A lack of osmosis will cause the vacuole and cytoplasm of the plant cells to shrink. The cell membrane may separate from the cell wall (plasmolysed). The cells become flaccid and the plant wilts.

A lot of osmosis will cause the vacuole and cytoplasm of the plant cells to expand. The cell membrane will push against the cell wall. The cells become turgid, supporting the plant. Lysis may also occur where the cell bursts.

Water absorption in roots:

Osmosis occurs to bring water from the soil where there is a high water potential and to the root hair cells which have a lower water potential. This occurs through a semi permeable membrane. However, soil particles are too big to pass through meaning only water is up-taken. Osmosis occurs through the entire root, going through the epidermis, cortex, endodermis until it reaches the xylem where water is carried up through transpiration.

Xylem:

•    Used to transport water and minerals towards the plant (one way).

•    A hollow tube of dead cells.

•    Contains lignin which makes the tube waterproof, allowing it to transport water.

Phloem:

•    Used to transport sugars and amino acids (two ways).

•    Contains sieve cells and tubes for mass movement.

•    Does not contain a nucleus so need companion cells to supply it with genetic information.

The xylem and phloem join together to form a vascular bundle. In the roots there is one massive vascular bundle called a stele. In the stem there are smaller vascular bundles.

Transpiration is the evaporation of water in aerial parts. A transpiration stream is the movement of water through the xylem through transpiration.

1.    Water between the palisade and spongy cells evaporate due to the heat from sunlight.

1.    This creates a vacuum, meaning water rises in the xylem.

2.    Water vapour diffuses into spongy cells and is used in photosynthesis.

3.    Unused water vapour diffuses out via the stomata.

Transpiration is needed for:

•    Transporting water for photosynthesis.

•    For cells to remain turgid.

•    To transport minerals.

•    To act as a rolling mechanism.

Factors affecting transpiration:

1.    More heat = More energy = Faster evaporation = More transpiration

2.    Higher humidity = More water molecules in air = Gentler concentration gradient = Less transpiration

3.    Higher wind speed = Water molecules are distributed = Steeper concentration gradient = More transpiration

4.    More sun = More heat = Stomata opens = Allows more water vapour to leave the leaf = More transpiration

Using a petometre you can determine the rate if transpiration

Weight petometre: when a plant transpires it loses water so it loses weight. Therefore, if you have a plant with no other way of losing weight other than transpiration (layer of soil, plastic bag), on a scale you can measure the rate of change and therefore the rate of transpiration.

Volume petometre: a bubble of gas is allowed to flow up a tube with a plant shoot. The rate at which it transpires up the then is measured and shows the rate if transpiration.

Minerals are taken up by plants, however, most of the time the concentration gradient is too low so diffusion cannot occur. Therefore, active transport is used. This uses chemical energy and carrier proteins to take in mineral salts.

A deficiency in minerals salts can cause diseases:

	Nitrates	Potassium Ions	Phosphate ions	Magnesium
Uses	DNA	Enzymes	Cell membrane	Chlorophyll
	Amino acids
Deficiency	Stunted growth	Yellow leaves	Poor root growth	Yellow leaves
Symptoms	Older leaves turn yellow	Dead spots	Young leaves turn purple

Transport in Humans:

The Blood Contains…

•   Plasma

•   Red blood cells (erythrocytes)

•   White blood cells (lymphocytes and phagocytes)

•   Platelets

Plasma:

Plasma is involved in the transport of carbon dioxide, digested food, urea, hormones and heat energy. Many substances are dissolved in plasma such as mineral salts.

Red Blood Cells:

Adaptation	Explanation
Contains haemoglobin	Used to combine with oxygen to form oxyhaemoglobin. This allows oxygen to be transported.
No nucleus	Leaves more space fir haemoglobin so that more oxygen can be transported.
Biconcave shape	Allows for a more efficient exchange of oxygen in and out of cells by increasing surface area.
Thin	Short diffusion pathway increases the rate of diffusion.
Flexible	This allows it to squeeze through blood capillaries.

The Antibody/Antigen reaction:

1.    Lymphocytes recognise individual marker chemicals called antigens on the surface of the pathogens.

2.    Lymphocytes’ receptor proteins bind with the antigens.

3.    When it binds the lymphocytes divide rapidly, producing millions of the same type of lymphocyte that is capable of recognising the microorganism.

4.    Most of this occurs with B and T lymphocytes.

5.    Most B-lymphocytes begin to produce antibodies which bind with the antigens, causing the pathogens to clump together. This makes it easier for phagocytes to ingest it through phagocytosis where pseudopodia enclose the pathogen. Some antibodies also cause the pathogens to burst apart. Some also develop into memory cells which remain for a long time and if the cells re-infect, the memory cells will start to reproduce and produce antibodies. Because of this the secondary immune response is much faster than the primary.

6.    T-lymphocytes destroy our own cells. These cells have become infected with a virus or are cancerous. This is done through releasing chemicals that “punch a hole” in the cell or activates a “programmed cell death” that is put into the genetic coding of every cell. Some also become memory cells like B-lymphocytes.

Vaccines:

These are a form of an artificial active immunity and works by injecting a person with an “agent” that carries the same antigens as a specific disease causing microorganism. This works by artificially creating an antigen/antibody reaction. This can be achieved by injecting…

•   An attenuated (weakened) strain of the actual microorganism (e.g. polio, TB and measles)

•   Dead microorganisms (e.g. whooping cough, typhoid)

•   A modified toxin of the bacteria (e.g. tetanus)

•   Just the antigen (e.g. Influenza)

•   Harmless bacteria, genetically engineered to carry the antigen of a different disease carrying microorganism.

Platelets:

Exposure to air stimulates the platelets and damaged tissue to produce chemicals. This causes the soluble protein fibrinogen to change into an insoluble fibre of a protein called fibrin. Fibrin forms a network across the wound, trapping the red blood cells and forming a clot. This prevents further loss of blood and entry of pathogens. The clot will develop into a scab which protects the damaged tissue while the new skin grows.

Heart:

 

How the heart works:

1.    Blood enters the atria.

2.    The walls of the atria contract, raising pressure and forcing open the bicuspid and tricuspid valves.

3.    When the ventricles fill with blood, the ventricles contract, raising pressure and closing the valves.

4.    The ventricles continue to contract and raise pressure. This forces the semilunar valves (pulmonary valve and aortic valve) to open.

5.    Blood flows into the aorta which carries blood to parts of the body and the pulmonary artery which carries blood to the lungs.

6.    High pressure in the aorta and pulmonary artery closes the semilunar valves and the process restarts.

Heart attacks are caused when the coronary artery is blocked completely meaning the heart muscles will stop contracting. This blockage is usually caused by a buildup of fat called an atheroma. Many factors can make heart attacks more likely:

1.    Heredity

2.    Permanent high blood pressure/hypertension puts more strain on the heart muscles as it has to work harder to pump blood.

3.    Diet - a diet rich in fats raises cholesterol. High cholesterol and fats creates the atheroma which can block the coronary arteries.

4.    Smoking - nicotine constricts blood vessels, raises blood pressure, speeds up the heart rate and increases blood cholesterol.

5.    Stress - hormones released during stress constricts blood vessels, raising blood pressure.

6.    Lack of exercise - regular exercise reduces blood pressure and strengthens the heart.

Heart rate:

Your heart rate increases during exercise to supply oxygen needed for the increased need for aerobic respiration to release more energy to be supplied to the muscle. This occurs as the aorta and the carotid artery detects extra carbon dioxide from the exercise and sends a signal to the medulla in the brain. The medulla sends impulses along the acceleration nerve. When carbon dioxide production slows, the medulla sends impulses along the decelerator nerve.

Arteries:

1.    Used to carry food away from the heart.

2.    Small lumen (central cavity).

3.    Thick wall with thick muscle fibres and elastic tissue.

Vein:

1.    Used to carry blood to the heart.

2.    Large lumen (central cavity).

3.    Thin wall with little muscle fibres and elastic tissue.

4.    Have valves which prevents the back-flow of blood.

Capillaries:

1.    Carry blood through organs and between cells.

2.    Capillary walls are one cell thick and allow substances to diffuse in or out.

Circulation System: