Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane.
Define active transport.
Active transport is the movement of particles against the concentration gradient (i.e: from a low to a high concentration).
Why does active transport require energy?
Because the particles are being absorbed against the concentration gradient.
What do most sports drinks contain?
-Water➡️To replace water lost when sweating.
-Sugar➡️To replace sugar used for energy release in exercise.
-Mineral ions➡️To replace those lost in sweating.
Why are isotonic sports drinks marketed as ideal for endurance sports?
Because an isotonic drink is taken up by the body as quickly as water, due to the drink concentration matching the body fluids.
What is an exchange surface and what features make them efficient?
Large, complex organisms have exchange surfaces to obtain all the food and oxygen they need.
Efficient exchange surfaces have a large surface area, thin walls/short diffusion path and an efficient transport system (i.e: the blood supply in animals).
How does air travel through the lungs?
1. Air passes into the nasal cavity, where dust and bacteria are filtered out by sticky mucus.
2. The air is drawn down the trachea, which is kept open by rings of cartilage.
3. At the bottom of the trachea it divides into two bronchi.
4. Each bronchus subdivides again into a mass of fine branches known as bronchioles.
5. These end in tiny hollow bags with bulb-like pockets called alveoli in which gases are exchanged.
6. Blood flowing through capillaries absorbs oxygen and releases carbon dioxide which diffuses back into the alveoli.
How are alveoli adapted to be efficient gaseous exchange surfaces?
-Alveoli are folded➡️more surface area for gaseous exchange to occur.
-The walls of alveoli are only one cell thick➡️shorter the diffusion distance.
-The outer surface of alveoli are covered by a dense network of capillaries➡️good blood supply.
-The capillaries themselves have thin walls➡️gases can diffuse in and out of them quickly.
-Alveoli are well ventilated so fresh oxygen is always present➡️concentration is always higher in the alveoli (steep diffusion gradient) so more diffusion of oxygen into the blood occurs.
Where in the body are the lungs situated?
The lungs are situated in the thorax, inside the ribcage and above the diaphragm, which separates the lungs from the abdomen.
What happens when we breathe in?
1. The muscles contract.
2. The ribcage moves up and out and the diaphragm flattens.
3. The volume increases.
4. The pressure decreases and air is drawn in.
What happens when we breathe out?
1. The muscles relax.
2. The ribcage moves down and in and the diaphragm becomes domed.
3. The volume decreases.
4. The pressure increases and air is forced out.
Why might a person not be able to get enough oxygen into their bloodstream?
-If the alveoli are damaged➡️the surface area for gas exchange is reduced.
-If the tubes leading to the lungs are narrowed➡️less air can be moved through them.
-If the person is paralysed➡️their muscles will not work to pull the ribcage up and out.
What types of breathing aid have been developed?
-The 'iron lung' was used for people with polio who were paralysed. The person's chest was sealed in a metal cylinder which got the person to breathe in and forced air out using negative pressure.
-Breathing aids which force measured amounts of airs into the lungs using positive pressure.
What are villi?
Villi are an efficient exchange surface for the absorption of the soluble products of digestion by diffusion or active transport.
How are villi adapted to be efficient exchange surfaces?
-Finger-like with large surface area➡️more surface area for exchange to occur.
-Thin walls, only one cell thick➡️shorter diffusion distance.
-Contain blood capillaries to carry away absorbed food molecules.
What are the stomata and what is their purpose?
The stomata are holes in the lower epidermis which allow carbon dioxide to diffuse into the leaf from the atmosphere.
What gases diffuse in and out of leaves and how?
-Oxygen: needed for respiration and a waste product of photosynthesis.
-Carbon dioxide: needed for photosynthesis and a waste product of respiration.
How is the leaf well adapted?
-Leaf is thin➡️Short diffusion distance.
-Waxy cuticle➡️To prevent water loss.
-Palisade mesophyll close to the top of the leaf➡️Closer to sunlight which is used in photosynthesis.
-Spongy layer has air spaces➡️Easier for CO2 to diffuse to the palisade layer.
-Cells are not tightly packed➡️Large surface area available for gas exchange.
-Guards cell open and close stomata➡️To control water loss.
What do Xylem tubes do?
Transport water and minerals to leaves.
What do Phloem tubes do?
Transport sugars from the leaves to growing regions and storage organs.
How is water taken in, in plants?
By the roots using osmosis.
How is water lost in plants?
Transpiration➡️Water evaporates from the leaves through the stomata.
When is transpiration more rapid?
In hot, dry, windy or bright conditions.
How does wilting reduce water loss?
The leaves collapse and hang down, which reduces the surface area.
Plant roots absorb water mainly by osmosis.
Plant roots absorb ions mainly by active transport.
Explain why roots need to use the two different methods to absorb water and ions (4marks).
The solution in the soil is more dilute (1) so water moves from a dilute to a more concentrated region (1).
The concentration of the ions in soil is less that in roots (1) so energy is needed to move ions (1).
What is meant by the transpiration stream?
Movement of water from roots via xylem to the leaves.