Exchange of Materials Flashcards
What is Osmosis?
The movement of water
From an area of high concentration to an area of low concentration along a concentration gradient
From more dilute solution to higher concentration
What does osmosis occur across?
A partially permiable membrane
What is the movement of water molecules performing osmosis like?
Random
What does osmosis not require from the cell?
Energy
Cells may need to absorb substances in short supply. To do this, they may have to absorb susbtances…
…against the concentration gradient
What is active transport?
The movement of susbtances across either a cell membrane or against a concentration gradient
It requires energy because of this
Where does the energy for active transport come from?
Respiration
How do root cells use active transport?
They absorb mineral ions from dilute solutions in the soil
How do the kidneys use active transport?
Glucose can be reabsorbed in kidney tubes
What specific substance dos active transport use?
A transport protein
It rotates, using energy
What happens if you sweat a lot or do not drink enough water? (Or eat a lot of salty food)
You may become dehydrated
What do sports drinks contain and why?
- Water to replace water lost by sweating
- Sugar to replace sugar used for respiration in exercise
- Mineral ions to replace those lost by sweating
What does isotonic?
Having the same concentration of solutes as another solution
What does it mean if a sports drink is isotonic?
The concentration of sugar, water, and mineral ions in the drink matches those in the body
For normal levels of exercise, what might be just as effective as a sports drink?
A drink of water
What do large organisms need and why?
Exchange surfaces
They need these to obtain all the food and oxygen they require
What makes an exchange surface efficient?
- Large surface area
- Thin walls or short diffusion path
- Efficient transport system - bloody supply in animals
What form of exchange takes place in the lungs?
The gaseous exchange
What are alveoli and how do they make the gaseous exchange more efficient?
Tiny air sacks. They have:
- Thin walls
- Large surface area
- Good blood supply
Why are the lungs ventillated and what does this mean?
Air is moved in and out
This maintains a steep diffusion gradient
How does oxygen enter/carbon dioxide leave the blood surrounding the alveoli?
They diffuse into the many capillaries surrounding the alveoli
Where are the lungs situated?
In the thorax
Describe the position of the lungs
In the thorax, inside the ribcage, above the diaphragm
The diaphragm seperates the lungs from the abdomen
What happens when we breathe in?
- The intercostal muscles between the ribs + diaphragm contract
- The ribcage moves up + out and the diaphragm flattens
- The volume of the thorax increases
- The pressure of the thorax decreases and air is drawn in
What happens when we breathe out?
- The intercostal muscles between the ribcage + diaphragm contract
- The ribcage moves down + in and the diaphragm becomes domed
- The volume of the thorax decreases
- The pressure increases and air is forced out
Why might someone not be able to get enough oxygen into their bloodstream?
- The alveoli are damaged and the surface area for gas exchange is decreased
- The tubes leading to the lungs are narrowed so less air can move through them
- The person is paralysed so their muscles will not work to pull the ribcage up and out
How does the ‘iron lung’ work?
- Person lay with chest sealed in a large metal cylinder
- When air was drawn out of the cylinder, the person’s chest moved out and they breathed in
- The vacuum which was formed inside the cylinder created a negative pressure
- When air was pumped back in to the cylinder, it created pressure on the chest and forced air out of the lungs
What is negative pressure?
A system where the external pressure is lower than the internal pressure
What is positive pressure?
A system where the external pressure is higher than the internal pressure
Who was the iron lung used for?
People with polio who has been left paralysed as a result of the disease
What type of artifical breathing aids use positive pressure?
Breathing aids which force measured amounts of air into the lungs
Bags of air linked to masks can force air down the trachea
Why might you use a positive pressure aid instead of a negative pressure aid?
- Smaller
- Easier to manage in the home
- Can be linked to computers for control
What is the exchange surface for food molecules in the small intestine?
Villi
What are villi and how do they work?
Small, finger-like projections which increase surface area for absorbtion to take place
The walls are very thin and have many capilliaries close to them
Rich blood supply provides a steep concentration gradient
Soluble products of digestion can be absorbed either by diffusion or active transport
How do gasses diffuse in and out of leaves?
Through tiny holes called stomata
The size of these is controlled by the guard cells which surround them
What gases diffuse in and out of leaves?
Oxygen - needed for respiration and a byproduct of photosynthesis
CO2 - Needed for photosynthesis and a waste product of respiration
What does the movement of gases in out out of the leaf depend upon?
Which process (respiration or photosynthesis) is taking place the most quickly
What do plants also lose through the stomata?
Water vapour due to evaporation in the leaves
In what ways are the leaves an efficient exchange surface?
They are very flat and thin so the gases do not need to diffuse very far
There are also internal air spaces
If plants lose water faster than it is replaced by the roots, what might the stomata do?
Close to prevent wilting
How do root hair cells provide an efficient exchange surface?
Increase the surface area of roots for the absorption of water and mineral ions
Describe the structure of the leaf and what each layer does
- Waxy cuticle on upper epidermis - waterproof which stops water loss
- Palisade layer
- Spongy layer - Cells not packed tightly, air spaces, large surface area for gas exchange
- Lower epidermis with guard cells - open and close stomata to control water loss
What is the transpiration stream?
The movement of water through the plant.
Goes from the roots to the leaves as a result of evaportation from the surface of the leaves
When is evaportation in plants more rapid?
- Hot
- Dry
- Windy
- Bright
Any of these conditions
What can be used to show how the uptake of water by a plant changes in different conditions?
A potometer
It gives you a good idea of the water lost by transpiration
What is wilting?
The process by which plants droop when they are short of water or too hot
Reduces further dehydration and prevents cell damage by decreasing surface area
