Osmosis And Plant Transport Flashcards
Osmosis definition
Osmosis is the diffusion of water molecules from a dilute solution to a more concentrated solution, across a selectively permeable membrane
Selectively permeable membrane
A selectively permeable membrane has holes in it that permit water molecules through but are too small to allow larger molecules through.
Visking tube
Osmosis can be demonstrated by using visking tubing filled with a solution and placed in a beaker of pure water.
Dilute solutions
Dilute solutions have a high concentration of water molecules
Concentrated solution
Concentrated solutions have a low concentration of water molecules
What happens to water molecules during osmosis
Initially, there is a larger number of water molecules in the more dilute solution than the concentrated solution. Some of the water molecules randomly diffuse across the selectively permeable membrane into the more concentrated solution. Eventually the molecules end up more evenly distributed.
Plant cells placed in high concentrated solution
Water has left the cell by osmosis because the solution surrounding the cell is more concentrated than the cytoplasm inside the cell.
The cytoplasm has pulled away from the cell wall
The cell is plasmolyse
Plant cell placed in medium concentration
The cells cytoplasm is the same concentration as the solution surrounding the cell.
There is no net movement of water
Plant cell placed in low concentration
We’re has entered the cell by osmosis. ThI cytoplasm is more concentrated than the very dilute solution surrounding the cell.
The cytoplasm is pushing against the cell wall
The cell is turgid
Lysis
In dilute solutions, osmosis can cause animal cells, such as red blood cells, to swell up and burst.
Crenation
In concentrated solutions, water loss causes the cell to shrink.
Animal cells placed in high concentration
Water has left the cell by osmosis because the concentration of the solution outside the cell is more than the concentration in the cell.
The cell becomes crenated as the cytoplasm pulls away from the cell membrane
Animal cell placed in medium concentration
The cell cytoplasm is at the same concentration as the solution surrounding the cell.
There is no net movement is water
Animal cells placed in Low concentration
Water has entered the cell by osmosis, pushing the cytoplasm against the cell membrane. Because the cell has no cell wall it bursts as it becomes turgid
The cell is destroyed
Why use a ruler when measuring potato cylinder
It has smaller divisions so you can measure in millimetres
Two factors to control during potato cylinder investigation
> The volumes of liquids in each beaker
>The same potato and size
How would you know if water have moved out of potato
Mass decrease or length decrease
Why is necessary to calculate percentage mass change
To compare the results
How can you improve the potato cylinder experiment
> Measuring to more than one decimal place
>Repeat experiment more than once
What fills the spaces between the membrane and cell wall.
Sugar solution
Why is water important
> Support
Transport
Photosynthesis
Transpiration
Support
We know that when plant cells absorb water they become turgid
Transport
Water is a solvent, many substances dissolve into water. This allow easy transport from one part of the plant to another
Photosynthesis
Water is an reactant in this process
Transpiration
A process that results from the evaporation of water from the surface of the leaf. Important as it keeps the steer moving through the plant
Transpiration
Transpiration is the evaporation of water from mesophyll cells followed by diffusion through air spaces and the stomata
Stage 1: transpiration
Water diffuses front the soil into the roots. Roots are covered in tiny projections called root hair cells. These structures increases the surface are of the roots
Stage 2:transpiration
Water travels up the stem of the xylem. It diffuses from an are of higher concentration the an area of lower water concentration
Stage 3: transpiration
Water travels through veins into the leaves. It then diffuses out of the veins into cells and air spaces. From theses spaces, water evaporates through the stomata, into the air
Stage 4: transpiration
The loss of water through transpiration in the leaves set up a concentration gradient, continuously pulling water form the soil into all parts of the plant
Factors affection the rate of transpiration
> Humidity (amount of moisture in the air)
Temperature
Wind speed (air movement)q
Humidity
Humid environments, such as rainforests, have high levels of water vapour in the air. This decreases the rate of transpiration because the air is already saturated with water. Transpiration will decrease when humidity increase
Temperature
High temperatures heat the leaves and cause water to evaporate more quickly. Warm air is also able to absorb more water vapour than cool air. This means a temperature increase will increase the rate of transpiration
Wind speed
When it’s windy, air saturated with water vapour is quickly moved away from the plant and replaced by drier air. The water concentration in the air will stay lower than in the plant, and this increase transpiration
Surface area
A greater surface area means that there are more stomata and therefore more water can be lost
Therefore the greater the surface area the greater the rate of transpiration
How the rate of transpiration can be measured
> Bubble/water uptake potometer
>Weight potometer
Two precautions taken when using water uptake potometer
> cut the shoot under water to prevent air entering the xylem
>the whole system needs to be air tight. There should be no air bubbles other than the one on the scale
How to stimulate environmental conditions
Wind speed: fan
Humidity: place a bag over the plant
Temperature: heater
The leaf and transpiration
Leaves represent main site of transpiration
Water escapes via the stomata. No most plants the number of stomata is directly linked to how quickly water is lost.
Leaf and transpiration experiment
Weigh at the start- record initial mass in grams Hang up Leave for 24hours Reweigh Calculate percentage change in mass
Purpose of reservoir in water uptake potometer
To reset the bubble
