Paper 1 cells 3 Flashcards
Define diffusion?
Diffusion is the spreading of particles of any substance in solution (or particles of a gas) resulting in net movement from an area of higher concentration to an area of lower concentration
Where can diffusion happen?
It can happen in a gas, liquid, or across a membrane
Explain net movement?
Net movement is when movement of particles is random, so some will be moving towards the higher concentration area, but more will be moving towards the lower concentration area.
How do you calculate the net movement?
Net movement = particle moving in - particles moving out
What determines the rate of net movement?
- Concentration gradient
- temperature
- Surface area
Explain what how a concentration gradient helps in diffusion?
The greater the difference in concentration between the two areas, the faster diffusion will be.
We say that diffusion occurs down a concentration gradient
Explain why the temperature is affected in diffusion ?
As the gas or solution heats up, the particles gain more kinetic energy and move around faster.
This increases the random movement of the particles and enables them to diffuse more rapidly.
Explain why a large surface area is better in diffusion?
- Dissolved substances move into and out of our cells through the cell membrane
- Our membranes allow only some materials to pass through and are called partially permeable
- By increasing the surface area through which the particles can move, diffusion can occur faster
Explain the diffusion of oxygen.
Air in lungs (high concentration) —
Explain the diffusion of carbon dioxide
CO2 from respiring cells (high concentration)—
Explain gaseous exchange
The movement of O2 and CO2 in opposite directions. Also known as respiration
Explain the diffusion of glucose
Digested food in intestines (high concentration)—
Explain the diffusion of urea
Created by breaking down amino acids in the liver (high concentration)—
What’s the relation ship between the size of an organism and the surface area to volume ratio?
The larger the organism, the smaller the surface area to volume ratio
Why do we have specialised exchange surfaces?
In order to speed up the transport of oxygen and glucose to respiring cells and removal of waste, specialised exchange surfaces are created to increase the surface area
Who exchanges substances faster by diffusion and why, bacteria or animals?
Bacteria, because they’re single cellular so they have a larger surface area to volume ratio
Why are animals slow at exchanging substances by diffusion?
Because they’re multicellular organisms so they have a small surface area to volume ratio
Give 3 ways to adapt for better diffusion and why?
- Increase the surface area, so more particles can move at once
- Have a short diffusion distance the particles have to travel
- Increase the steepness of the concentration gradient to speed up the net flow of particles
Example why the lungs are so good at diffusion (4)
- A large number of small alveoli, creates a large surface area for rapid diffusion of gases
- A rich capillary blood supply brings fresh blood to the alveoli to maintain steep diffusion gradient for rapid diffusion
- Ventilation (breathing) refreshes the air in the lungs to maintain a steep diffusion gradient for rapid diffusion
- A thin alveolar wall gives the shortest diffusion distance for the gases
Give reason the small intestine is good at diffusion? (3)
- The lining of the intestine is folded into thousands of villi, which in turn have numerous microvilli on their surface. They give the digestive system a huge surface area for absorption
- They have a rich capillary blood supply to remove absorbed nutrients and maintain a steep concentration gradient
- The walls are only one cell thick to keep the diffusion distance short
Gives reasons why plant roots are good at diffusion compared to other parts of the plant?
- the top of the roots are covered in root hair cells
- these are the only part of the root that actually absorb water and nutrients
1. Their hair -like projection increases their surface area for absorption
2. Transpiration in the leaves continuously pulls water up the plant, creating a steep concentration gradient.
3. There is a short distance from the edge of the root to the xylem in the middle
Give reasons why plant leaves are good at diffusion/osmosis? (2)
- The thin leaf shape minimises the diffusion distance for gases
- there are pores in the bottom surface of the leaf called stomata to allow carbon dioxide to diffuse into the leaf and oxygen out The air spaces in the spongy layer exposes a large surface area for gaseous exchange
Define osmosis
Osmosis is the diffusion of water from a dilute solution (where there is a high concentration of water) to a strong solution (where there is a low concentration of water) across a partially permeable membrane
Define partially permeable membrane
Let’s stuff through small holes
Define dilute solution
Where there is a high concentration of water
