| What is the definition of osmosis? | Osmosis is the diffusion of water molecules, from a region where the water molecules are in higher concentration, to a region where they are in lower concentration, through a partially permeable membrane |
| Osmosis in: Plant Cells | - Root hair cells, if the soil is wet or moist, will also take up water by osmosis
- Leaf cells of land plants, unless it is raining or the humidity is high, will have a tendency to lose water
- Plant cells have a strong cellulose cell wall which is fully permeable and supports the cell, stopping it from bursting as it gains water
- Aquatic, freshwater plants placed in the sea, or a seaweed in a rock pool where the water evaporated in the Sun, would also lose water by osmosis |
| Osmosis in: Animal Cells | 1) Animal cells also take in and lose water by osmosis. They do not have a cell wall, so will change size and shape when put into solutions that are at a different concentration to the cell contents. Red Blood cells can:
- lose water and shrink
- gain water, swell and burst in a more dilute solution
2) In animals, the concentration of body fluids – blood plasma and tissue fluid – must be kept within strict limits, if cells lose or gain too much water by osmosis, they do not function efficiently |
| PRACTICAL: Osmosis | 1) Prepare a range of sucrose (sugar) solutions - could be sodium chloride (salt). Measured in 'mol dm-3'. E.g. 0.2 mol dm-3 to 1.0 mol dm-3.
2) Set up a series of boiling tubes with each of these solutions. 1 will contain distilled water (0.0 mol dm-3 of sucrose) - it'll act as the control in the experiment. Make sure each tubes concentration is labelled
3) Prepare blank results table. Make sure potatoes mass' are not mixed up when recording them. Each cylinder will have a different mass before and after investigation
4) For each sucrose concentration, repeat the investigation for several potato cylinders - makes experiment repeatable as not all potatoes behave in the same way, also means anomalies can be identified and ignored when calculating mean |
| Give 4 ways alvioli are adapted for exchanging substances? | 1)High surface area to volume ratio (more points of entry for gases compared to capacity or organism)
2)Moist lining
3)one cell thick minnimising distance gases have to diffuse
4)good blood supply |
| Give 3 ways villi are adapted for exchanging surfaces | 1)High surface area to volume ratio
2)single layer of surface cells minnimising distance gases have to diffuse
3)good blood supply |
| What key thing would happen if a plant didnt have guard cells? | The plant would wilt. |
| Descreibe the gaseous exchange in fish | 1)water enters the fish through the mouth and reaches the gills oxygen diffuses from the water into the blood and carbon dioxide diffuses from the blood |
| Give 4 ways gills are adapted for gaseous exchange? | 1)Each gill consistss of plates called gill filiament, each filliament covered in tiny structures called lamelle meaning the have very large surface area.
2)Lots of blood capiliaries speeding up diffusion.
3)Thin surface layer minnimising distance gases have to diffuse.
4)Blood and water travekin different directions maintaining high concentration gradient so as much oxygen diffuses as possible. |
