B2.2 Flashcards
What is a surface area to volume ratio?
Smaller organisms have a high SA : volume so can rely on diffusion to exchange. Diffusion is must faster as the distance is much smaller
Larger multicellular organisms have a low SA : volume and rely on large exchange systems. Transport systems are needed as the distance is too large
How do lungs maximise rate of diffusion of oxygen into the bloodstream?
Contain many alveoli which increase the SA
How does the small intestine maximise rate of diffusion?
Contain villi which increase the SA
Why do we need transport systems?
Once a required substance has diffused into the body it must be transported to where it is needed
Main one in animals is the circulatory system
Plants have xylem and phloem tubes
What is a circulatory system?
Humans have one made up the heart and blood vessels
As blood remains within the structures it is known as a closed system
What is a double circulatory system?
Blood flows through the heart twice during one circuit of the body
How does the circulatory system work?
- deoxygenated blood travels to the lungs from the pulmonary artery where oxygen and glucose diffuse into the blood and it become oxygenated
- the oxygenated blood returns to the heart (via the pulmonary vein) into the left atrium
- it is pumped into the left ventricle (muscle is very thick to pump blood at high pressure to aorta) down to the head and body where the oxygen and glucose diffuses out of the blood and CO2 into the blood
- the blood is now deoxygenated
- and travels up the vena cava and into the right atrium and down to the right ventricle
The blood is then pumped up the pulmonary artery and the cycle continues
What are blood vessels?
3 main blood vessels - arteries, veins and capillaries
Tubelike structures that transport blood around the body
Contain a hollow cavity called a lumen
What is an artery?
- has a thick outer wall
- thick layer of muscle and elastic fibres
- small lumen
- smooth lining
Carry blood away from the heart under HIGH pressure
What are veins?
- thin outer wall
- thin layer of muscle and elastic fibres
- large lumen
- smooth lining
Return blood to the heart, contain valves that stop the back-flow of blood
What are capillaries?
- very small lumen
- wall made of a single layer of cells
Link arteries and veins in tissues and organs
Form a network so every cell is close to a capillary - semi permeable
Why is the arterial wall thick and muscular?
To withstand the high pressure of blood that is pumped from the heart
Th wall expands and recoils to push the blood forward
Why are thick walls not required for veins?
Blood pressure is low in the veins
What is the heart made of?
Made of cardiac muscle
Contraction without receiving a nerve impulse from the brain
What are the 4 chambers of the heart?
Right and left atrium
Right and left ventricle
Valves separate the chambers
What is in blood?
Red blood cells - small biconcave cells that have no nucleus and contain haemoglobin to carry oxygen. Fit in the lumen of a capillary one at a time
White blood cells - make antibodies that fight off disease
Plasma - straw coloured liquid that flood cells float in. 90% water
Platelets - help blood clot
How do plants transport materials?
Has two transport systems:
Xylem tissue - transports water and mineral ions from the roots to the stem, leaves and flowers. Made of dead cells, hollow lumen, and thick cell wall. No cell content so is a continuous column for water to move through
Phloem tissue - transports dissolved sugared from the leaves to all other areas of the plant. TRANSLOCATION (movement of glucose form the leaf to other parts of the plant by the phloem)
Phloem and xylem are found near each other and form a vascular bundle
What is the structure of xylem?
Made of xylem cells, no cell walls
A tube which water and dissolved ions can flow through
Has thick walls stiffened with lignin
One way for molecules to travel
What is the structure of phloem?
Made of living cells
Cell walls of these cells don’t fully break down but form sieve plates which allow dissolved sugars to pass through
How do the vascular bundles provide support?
- in the leaf they from a network that supports the softer leaf tissue
- in the stem they are located around the outer edge to provide the stem with strength to resist breeze bending
- in the root they’re found in the centre enabling the root to act as an anchor
What is transpiration?
Water moves through the xylem vessel because of transpiration
Loss of water from the plants leaves
Water lost must be replaced by the uptake through the roots
What is the transpiration stream?
Constant flow of water from the roots through the xylem and out the leaves
How does water enter the xylem?
Active transport of mineral ions into the root hair cells to create a lower WP so water will move in by osmosis
How is water lost from the leaves?
The stomata allows CO2 to diffuse in for photosynthesis
Guard cells allow stomata to open and close
While the stomata is open water vapour can leave through the stomata by diffusion
How does transpiration stream work?
Look at diagram on pg81
Why do plants wilt?
If a plant loses water faster than it takes it in
Leaves collapse and droop which reduces the SA for evaporation
The stomata closes and prevents photosynthesis and loss of water
Will eventually die
What are the factors affecting transpiration?
Light intensity - increases rate as more water evaporates
Temperature - water evaporates quicker, diffusion becomes more rapid
Air movement -concentration gradient increases so diffusion is faster
Humidity (quantity of water in the air) - lower humidity mean concentration gradient increases so water diffuses out quicker
Equation for measuring rate of transpiration?
Rate of movement = distance/time
