Movement of substances in and out of cells Flashcards
What are the three movements of substances in and out of cells?
- Diffusion
- Osmosis
- Active transport
What is diffusion?
The net movement of particles from an area of high concentration to an area of lower concentration until a uniform concentration is achieved
Why does diffusion happen in both liquids and gases but not solids?
The particles in these substances are free to move randomly
The bigger the different in concentration in diffusion….
The faster the rate of diffusion
What type of molecules can diffuse through cell membranes?
Small molecules like glucose, amino acids, water and oxygen. Big molecules like starch and protein cant fit through!
Particles in a cell membrane move from an area of…
Higher concentration to an area of lower concentration
If there are more particles on one side of the membrane…
Theres a net movement from that side
What is osmosis?
The net movement of water molecules across a partially permeable membrane from a region of higher water concentration to an area of lower concentration until a uniform water concentration is achieved.
Is osmosis a type of diffusion?
Yes
What is a partially permeable membrane?
A membrane with lots of very small holes in it - stops big molecules flowing through
Why can water molecules flow both ways through the membrane is osmosis?
Because the water molecules move around randomly all the time
If there is a net flow of water into a region with fewer water molecules in osmosis…
That solution becomes more dilute as the water tries to even up the concentration on both sides
What does the tissue fluid around our cells contain?
Water, oxygen and glucose that is squeezed out of the blood capillaries to supply the cell with everything they need.
If a cell is short of water…
It becomes concentrated - the solution outside is more dilute so water moves into the cell by osmosis
If a cell has lots of water…
The solution inside is more dilute - water is drawn out of the cell into the fluid outside by osmosis
What are plants supported by?
Turgid cells
When a plant is well watered…
The cells will draw water in by osmosis, and become plump and swollen (turgid)
What is turgid pressure?
The contents of the cell pushing against the cell wall supporting the plant tissue
What happens to a plant if theres no water in the soil?
The plant starts to wilt (droop) - the cells loose water therefore loose turgid pressure making them flaccid
Why doesn’t a plant totally lose its shape when it becomes flaccid?
The inelastic cell wall keeps things in position - it droops just a bit
What are plants supported by?
Turgid cells
When a plant is well watered…
The cells will draw water in by osmosis, and become plump and swollen (turgid)
What is turgid pressure?
The contents of the cell pushing against the cell wall supporting the plant tissue
What happens to a plant if theres no water in the soil?
The plant starts to wilt (droop) - the cells loose water therefore loose turgid pressure making them flaccid
Why doesn’t a plant totally lose its shape when it becomes flaccid?
The inelastic cell wall keeps things in position - it droops just a bit
What can you use to investigate diffusion in a non-living system?
Phenolphthalein - pH indicator. It is pink in alkaline solutions and colourless in acidic solutions and can be used with agar jelly
What is the method in the experiment for using the agar jelly?
- Make up agar jelly with phenolphthalein and dilute sodium hydroxide - jelly turns pink.
- Fill a beaker up with some dilute hydrochloric acid and cut out cubes using a scalpel.
- Put them into beaker of acid
What happens if you leave the agar cubes in the water for a while?
They eventually turn colourless as the acid diffuses into the agar jelly and neutralises the sodium hydroxide
How can you investigate the rate of diffusion with the agar jelly?
Change size of cubes - largest SA:VR will lose colour the quickest
How can you investigate osmosis in a living system?
Use potato cylinders
What is the method for using potato cylinders to investigate osmosis?
- Cut potatoes into equal cylinders
- Get two beakers: one should be very concentrated sugar solution and the other pure water
- Measure length of cylinders then leave for half an hour/an hour
- Measure length after time and compare the start and end results
If the cylinders have drawn water in by osmosis…
They should be a bit longer
If the cylinders have drawn water out…
They should have drunk a bit
How can you investigate osmosis in a non-living system?
Use visking tube
What is active transport?
The movement of particles against a concentration gradient from an area of lower concentration to an area of higher concentration using energy released during respiration
Give an example of when active transport is used in the body
In our digestive system - there is a low concentration of nutrients in the gut but a high concentration of nutrients in the blood
What does active transport allow?
For all the nutrients to be taken in by the blood, despite the concentration gradient being the wrong way. It is essential to stop us from starving
How do plants use active transport?
They get minerals from the soil (lower concentration) into the root hair cells (higher concentration)
What three main factors affect the movement of substances?
- SA:VR
- Temperature
- Concentration gradient
Is the rate of diffusion in diffusion, osmosis and active transport higher or lower in cells with a larger SA:VR?
Higher
Does a smaller cube have a larger or smaller SA:VR? And does it affect the rate of movement?
Larger SA:VR meaning that substances move in and out the cube faster
As temperature increases…
Substances move in and out of cells faster because they get warmer so have more energy and move faster
If there is a big difference in concentration gradient…
Substances move in and out faster between the inside and outside of the cell.
Does a big difference in concentration gradient affect active transport?
No becuase active transport is against its concentration gradient
