Chapter 2: Movement of Substances Flashcards
Define ‘diffusion’
It is the net movement of particles from a region of higher concentration to a region of lower concentraion down a concentration gradient
How does diffusion work? (Perfume example)
- Particles of the perfume evaporate from the surface of the spill and becomes gas.
- The gas particles have kinetic energy and are constantly moving around in all directions.
- They bump into one another and move about randomly.
4.This causes the gas to spread throughout the hosue until it reaches your nose and you smell it. - The gas spreads outwards through diffusion
Define ‘ concentration gradient’
It is the difference in concentration between two regions.
How do the particles become evenly spaced out during diffusion?
As particles of fluids are constantly moving about randomly, the particles will move down the concentration gradient and become evenly spread out after awhile.
What is the relationship between the concentration gradient and rate of diffusion?
The steeper the concentration gradient, the faster the rate of diffusion for that substance.
What happens if there is more than one substance dissolved in the same liquid in terms of diffusion?
The dissolved particles of one susbtance will diffuse independently of the others.
How does diffusion across a membrane work?
- The dissolved particles of copper (ll) sulfate will diffuse across the membrane to the left sid eof the beaker.
- The dissolved particles of potassium nitrate will diffuse across the membrane to the right side of the beaker.
- Eventually, there will be equal concentration of all particles on both sides of the membrane.
What are the factors affecting rate of diffusion?
- Diffusion distance
- Surface area-to-volume ratio
- Concentration gradient
What is the relationship between the diffusion distance and the rate of diffusion?
The shorter the diffusion distance, the faster the rate of diffusion
What is the function of cells being small in size?
To be able to move oxygen, nutrients and waste materials across their cell membrane fast enough to survive.
What is the relationship between the surface area-to-volume and the rate at which substances move in and out of the cell?
The greater the surface area-to-volume, the higher rate at which substances move in and out of it.
What is the relationship between the surface area and the rate of diffusion?
The larger the surface area, the higher the rate of diffusion.
What happens as a cell grows in size?
Its growth slows down and stops once it reaches its optimum size.
Why does that happen when a cell grows in size?
As the cell grows larger, the rate of oxygen and food intake slows down.
Why did the solution in arm A (10% sucrose solution) rises while the solution in arm B (5% sucrose solution) falls?
- Sucrose molecules cannot diffuse from A to B to make both solutions have the same level of sucrose molecules as they are too big to pass through the pores of the membrane
- Water molecules move from B to A as B has more water molecules per unit volume than A as B is a dilute solution that has more water molecules per unit volume than A, a concentrated solution of the same volume
- This results in A and B having the same solute concentration.
Define ‘osmosis’
The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.
When is a water potential gradient established?
When a partially permeable mebrane separates two solutions of different water potentials.
Why does a plant cell act differently from an animal cell when placed in solutions with differing water potentials?
Due to the presence of the cell wall in the plant cell.
What happens to an animal cell in a solution with HWP and explain why that happens.
It will swell and may even burst as it does not have a cell wall to protect it.
What happens when you place a plant cell in a solution with HWP (exam ans)?
- When a plant cell is placed in a solution of HWP, its vacuole has a LWP than the solution outside of the cell.
- By osmosis, the water molecules enter the cell through the partially permemable membrane.
- The cell expands and swells, becoming turgid
- As water molecules enter, the vacuole expands and pushes the cytoplasm against the cell wall.
- The cell does not burst as it is protect by its inelastic cell wall.
What happens to a cell in a solution of SWP?
It will stay the same as their cytoplasm will not its shape and size as the movement of water molecules is the same in both directions. Thus there is no net movement of water molecules in and out of the cell.
What happens when you place an animal cell in a solution with LWP?
- It will cause it to lose water
- The cell shrinks and spikes will appear on the cell.
- The cell will become dehydrated and die when placed in a solution of lower water potential.
What happens to a plant cell in a solution with LWP?
- When a plant cell is submerged in a solution with LWP, its vacuole has a higher water potential than the solution outside of the cell.
- By osmosis, the water molecules from the vacuole and the cytoplasm leave the cell through the partially permeable membrane.
- The cell decreases in size and becomes flaccid.
- As the cell loses water, its vacuole decreases in size
- The cytoplasm shrinks away from the cell wall and cell membrane plasmolysed.
Define ‘plasmolysis’
The shrinkage of the cytoplasm and cell membrane away from the cell wall
How can you restore a plasmolysed cell?
By placing it in water or a solution of HWP
Why is turgor important in plants?
It helps the plant to maintain the shape of soft tissues in plants.
What happens when there is a high rate of water loss from the plant?
The plant will lose their turgidity and wilt, causing the plant to receive lesser sunlight and thus producing less food for itself to survive
Why does the stomata of a plant cell close when the cell is flaccid? Tell me the pros and cons of the stomata closing.
The stomata becomes smaller and eventually closes. On hot days, this is good as this prevents more water loss through the stomata. However, usually this is bad for the plant as the plant will be unable to take in its usual amount of carbon dioxide to photosynthesise and it will be unable to release oxygen into the atmosphere.
Why is it bad too put too much fertiliser around the roots of plants?
The high concentration of soil will cause water to go out of the roots and into the soil via osmosis as the roots will have a higher water potenial than the soil. Inability of the roots to absorb water and continued evaporation of water from the leaves will cause the plant to wilt. Unless sufficient water is added to dilute the soil, the plant will eventually die.
Define ‘active transport’
It is the process in which energy is used to move the particles of a substance across a membrane against its concentration gradient, from a region of lower concentration to a region of higher concentration.
How does active transport occur in the intestine when you skip meals?
As the glucose levels in your intestine cells are higher than the glucose levels out side of the cell, glucose from outside enter the cell via active transport.
How does active transport happen in root hair cells?
Mineral salts take a different pathway to enter the root hair cells via active transport in order for the cell to have enough mineral salts to survive
