BIO 2 : MOVEMENT OF SUBSTANCES

What are some factors that can affect rate of osmosis ?

Water poential gradient , distance in which water molecules need to move , surface-area to - volume ratio.

What happens when a plant cell is placed in a solution of higher water potential ?

When a plant cell is placed in a solution of higher water potential , the cell sap has lower water potential than that of the solution outside the cell. By osmosis, water molecules enter the cell through the partially permeable cell membrane. As water molecules enter the cell , the vacuole increases in size and pushes the cytoplasm against the cell wall. The cell expands and becomes turgid.

What is turgor pressure ?

Pressure exerted by water in the vacuole

What is turgor ?

Turgidity of the cell with water.

What happens when an animal cell is placed in a solution of higher water potential ?

The animal cell may swell over even burst in a solution as it does not have cell wall to protect it.

What happens to a cell in a solution of same water potential ?

There will be no net movement of water molecules in and out of the cell as the movement of water molecules is the same in both directions.

What happens to a plant cell in a solution with lower water potential ?

The water molecules will leave the vacuole and cytoplasm by the partially permeable membrane via osmosis. As the cell loses water, the vacuole decreases in size. The cytoplasm shrinks away from the cell wall. The cell is plasmolysed. The cell decreases in size and becomes flaccid.

What is plasmolysis ?

The shrinkage of cytoplasm and cell membrane away from the cell wall.

How can a plasmolysed cell be returned to its original state ?

By placing it in water or a solution with higher water potential.

What happens when an animal cell is placed in a solution with lower water potential ?

It will cause the animal cell to lose water. The cell will shrink and spikes will appear, which is the process of crenating. It will become dehydrated and eventually die.

What is hypotonic ?

Higher water potential

What is hypertonic ?

Lower water potential

Why is turgor important in plants ?

Turgor plays an important role in maintaining the shape of soft tissue in plants. The young stems and leaves of herbaceous and non-woody plants are able to remain firm and erect. This is because of the turgor pressure within their cells. When there is a high rate of water loss from the cells, they lose their turgidity and the plant wilts. The movements of certain plant parts are due to changes in turgor. For example, changes in the turgor of the guard cells cause the opening and closing of the stomata.

What is soil solution ?

It is a thin film of water that surrounds individual soil particles. It usually contains dissolved mineral salts or ions.

Why is it not advisable to add too much fertiliser around roots of plants ?

The soil solution will become very concentrated and water molecules will move out of the roots by osmosis. Inability of the roots to absorb water , together with continued evaporation of water from the leaves, will cause the plant to wilt. Unless sufficient water is added to dilute the soil solution, the plant will eventually die.

What is active transport ?

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 where the particles are of lower concentration to a region where they are of higher concentration.

Where does active transport occur ?

Active transport occurs only in living cells because living cells respire. It is used during respiration that energy is released , and part of this energy is used in active transport.

Root hair cells have a high mineral ion concentration.Explain how this is maintained and its importance.

Since the root hair cell absorbs water, it needs to maintain low water potential. The root hair cell actively transports ion into inself, maintaining the concentration of the root hair cell to always high. Having a high concentration would lead to low water potential , hence causing water molecules to enter through its partially permeable membrane by osmosis. This would allow the root hair cell to absorb sufficient water for the plant for survival and helping the plant photosynthesize.

What does water potential mean ?

The tendency ( likelihood ) for water molecules to move from one place to another.

What is water molecules ?

water moving at a molecular level

What does net movement of water molecules mean ?

More water molecules moving across the partially permeable membrane in one direction more than the other.

What is osmosis ?

Net movement of water molecules from a solution of high to lower water potential across a partially permeable membrane.

How does surface area to volume ratio affect the rate of diffusion ?

the rate of movement of s substance across a cell membrane depends on how large the cell membrane is ( surface area of cell ). The ratio between the surface area and volume of a cell is - SAVR. The greater the SAVR of a cell , the higher the rate which substances move in and out of it ( higher rate of diffusion ). EG Some cells are specially adapted to absorb substances ( root hair cell ). These cells have long narrow protrusions. which increase the SAVR ratio of the cell membrane so more materials can be absorbed into the cell.

What is diffusion distance and how does it affect rate of diffusion ? State some examples

It is the distance which a substance diffuses. The shorter the diffusion distance , the less time needed for substance to travel , rate if diffusion is higher. EG Plant cells take in oxygen and remove carbo dioxide through diffusion. Exchange of oxygen and carbon dioxide in the lungs take place by diffusion. In both these examples , the diffusion distance is short , allowing diffusion to occur at a higher rate.

What are the factors that can affect the rate of diffusion ?

Temperature , concentration gradient , diffusion distance , surface area to volume ratio .

Describe diffusion across a permeable membrane .

A permeable membrane allows both the solvent and the solutes to pass through it. The dissolved particles on the right will diffuse across the membrane to the left side . The dissolved particles on the left will diffuse to the right side. Eventually , there will be equal concentrations of all particles on both sides of the membrane.

How do particles in different concentrations move ?

The particles of fluids ( liquids & gases ) posses kinetic energy which causes them to move continuously . As their movement is random , the particles will move , diffuse down the concentration gradient and become evenly concentrated after some time.

What is diffusion ?

Diffusion is the net movement of particles from a region where they are high in concentration to a region where they are low in concentration.( down a concentration gradient ) ( can happen acorss a membrane but it's not a requirement unlike osmosis )

Why is water a universal solvent ?

It served as a medium for biochemical reactions to take place in , and transporting soluble substances .

What is concentration gradient ?

It is the difference in concentration between 2 regions. The steeper the concentration gradient for a substance , the faster the rate of diffusion for that substance. The concentration of the substance in either region is not important , it's the difference in the concentration that is . I.E zero vs low ( not steep , small difference ) low vs low ( not steep ) high vs high ( not steep ) low vs high ( steep , large difference ) high vs zero ( steepest , largest difference )

How does temperature affect diffusion ?

The higher the temperature , faster vibrations of these particles due to kinetic energy.

Where can we see no net movement ?

It's when the number of particles in both directions are equal ( during dynamic equillibrum ). No diffusion is happening but the particles are still moving in both directions.

What is net movement ?

Net movement is what we see before the particles are in equal concentrations. More particles are moving in one direction that the number moving in the opposite direction.

What is volume ?

amount of space an object occupies

What is concentration ?

It's the proportion of a solute in its solvent ( ratio )

What movements of substances require energy and which ones don't ?

( don’t need input of energy ) passive process- Diffusion and osmosis ( need input of energy ) active process - active transport

What is the difference between passive and active process in movement of substances ?

Passive process occurs without input ( using ) energy , describes the movement of substances w/o using energy. Active process occurs requires ( using ) input of energy , describes movement of substances with energy.

What does dynamic equilbrum mean ?

dynamic - constantly moving , equillbrum - equal amount / concentrations when two amounts of concentrations are in equal amounts but are still constantly moving