Do smaller animals have a large or small SA:V?
What are the exchange systems/organs of single-celled organisms?
Substances diffuse directly into/out of the cell across its membrane. The diffusion rate is quick, as the distance the substances travel is small.
What are the exchange systems/organs of multicellular animals?
Specialised exchange systems are needed, as the diffusion distance is large. They have a low SA:V.
Do larger animals have a large or small SA:V?
If you have a low SA:V, what is your heat loss like?
If you have a high SA:V, what is your heat loss like?
If you have a compact shape, what is your SA:V like? Therefore, what is your heat loss like?
Low SA:V; therefore, slow heat loss.
How does gas exchange work in single-celled organisms?
They absorb/release gases by diffusion through the outer surface. They have a large SA, and a thin surface, so there is a short diffusion pathway. They have no gas exchange system.
How does gas exchange work in fish?
1) Water enters the fish's mouth and passes out through the gills.
2) Each gill is made of gill filaments, which have a large SA for gas exchange.
3) These have lamellae, increasing SA more. They also have many blood capillaries and a thin surface layer of cells to speed up diffusion.
4) Blood flows through the lamellae in one direction and water in the opposite direction. A large concentration gradient is maintained.
How does gas exchange work in insects?
1) Trachae are air-filled pipes insects use for gas exchange.
2) Air gets to the trachae through pores on the surface called spiracles.
3) Oxygen moves down its concentration gradient to cells. CO2 moves down its concentration gradient to the spiracles to be released.
4) Trachae have smaller trachioles which go to individual cells. They have thin, permeable walls.
5) Rhythmic abdominal movements are used to move air in and out of the spiracles.
How are gills adapted for gas exchange? Give five reasons.
1) Large SA provided by gill filaments/lamellae.
2) Thin epithelium - short distance between water and blood.
3) Counter-current maintains concentration gradient along the gills. Water is always next to blood with a lower concentration of oxygen.
4) Circulation replaces blood saturated with oxygen.
5) Ventilation replaces water as oxygen is removed.
How does gas exchange work in plants?
1) Gases move in and out through the stomata in the epidermis.
2) Stomata, controlled by guard cells, can open and close.
3) Gas exchange takes place in the surface of mesophyll cells.
How is water loss controlled in insects?
Insects can close their spiracles if they are losing too much water. They have a waterproof waxy cuticle around their body. Tiny hairs around the spiracles reduce evaporation.
How is water loss controlled in plants?
1) Water enters guard cells, making them turgid. Stomatal pore opens.
2) If the plant gets dehydrated, the guard cells lose water and become flaccid, closing the pore.
What are xerophytes?
Plants that are adapted for warm, dry, or windy habitats.
How is water loss controlled in xerophytes?
1) The stomata are sunk in pits, trapping air.
2) Curled leaves with stomata inside, protecting from wind.
3) Hairs on epidermis trap moist air around the stomata, reducing the concentration gradient of water.
4) Reduced number of stomata - water has fewer places to escape from.
5) Waxy waterproof cuticles on leaves and stem.
Do veins transport blood from the body to the heart or from the heart to the body?
From the body to the heart.
Do arteries transport blood from the body to the heart or from the heart to the body?
From the heart to the body.
What does the hepatic portal vein do?
Transports blood from the gut to the liver.
What does the hepatic artery do?
Transports blood from the heart to the liver.
What does the renal artery do?
Transports blood from the heart to the kidneys.
What does the renal vein do?
Transports blood from the kidneys to the heart.
What does the hepatic vein do?
Transports blood from the liver to the heart.
What are two features of the arteries?
1) Walls are thick and muscular. They have elastic tissue to cope with the high pressure from the heartbeat.
2) The endothelium (inner lining) is folded so that the artery can expand.
What are two features of arterioles?
1) They contract to restrict blood flow.
2) They relax to allow blood flow.
What are three features of veins?
1) Wide lumen - little muscle/elastic tissue.
2) They have valves to stop blood from flowing backwards.
3) Blood flow is helped by muscle contractions.
What are five features of capillaries?
1) Capillaries are branched off from arterioles.
2) They have a short diffusion pathway.
3) Walls are one cell thick.
4) There are many capillaries, so a large SA for gas exchange.
5) Networks of capillaries are called capillary beds.
What is tissue fluid for?
Cells take in oxygen and nutrients from the tissue fluid and release waste into it.
What happens at the start of the tissue bed?
The pressure in capillaries is greater than the pressure in the fluid. This forces fluid out of capillaries and into spaces around cells.
What happens as the fluid leaves the bed?
The pressure reduces in capillaries. The pressure is lower at the end of the bed, nearest to the veins.
What happens because of fluid loss in the capillary bed?
The water potential at the end of the bed is lower than the water potential in the fluid. Water reenters capillaries via osmosis.
Does tissue fluid contain red blood cells and big proteins?
No, because they are too large to be pushed out of capillary walls.
What happens to excess fluid from tissues?
It is drained from the tissues and into the lymphatic system, which dumps it back into the circulatory system.
Does soil or the xylem have a high water potential?
Name the process through which water travels in a plant.
Soil (high w.p.) --> root hair cells --> cortex --> endodermis --> xylem (low w.p.)
What is the symplastic pathway?
This pathway goes through the living parts of cells (cytoplasm). Cytoplasm --> plasmodesmata (small gaps in cell walls).
What is the apoplastic pathway?
This goes through the non-living parts of the root (cell walls). The walls are very absorbent and water can diffuse through them, as well as passing through spaces in between.
In the apoplastic pathway, what happens when water gets to the endodermis?
Its pathway is blocked by a Casparian strip - it now has to take the symplastic pathway. This is useful because it now has to go through a cell membrane, which controls the passage of substances.
Which pathway provides the least resistance - apoplastic or symplastic?
What is cohesion tension theory?
1) Tension is crated from water evaporating at the top of the xylem. This pulls more water into the leaf.
2) Water is cohesive - when some molecules are pulled into the leaf, others follow. The column of water in the xylem moves upwards.
What is the role of root pressure in the transportation of water in the xylem?
When water is transported into the xylem from the roots, it creates pressure and moves the water in the xylem upwards. This pressure is weak.
What is transpiration?
The evaporation of water from a plant's surface.
What are the four factors affecting transpiration?
How does light affect transpiration?
The lighter it is, the faster the rate of transpiration. This is because the stomata are open when it is light.
How does temperature affect transpiration?
The warmer it is, the faster the rate of transpiration. Water molecules have more energy, so they evaporate faster.
How does humidity affect transpiration?
The lower the humidity, the faster the rate of transpiration. If air around the plant is dry, the concentration gradient between the leaf and the air increases.
How does wind affect transpiration?
The windier it is, the faster the rate of transpiration. Water molecules from around the stomata are blown away, increasing the concentration gradient between the stomata and the air.