OSMOSIS AND DIFFUSION - (PS 7) Flashcards
Distinguish between diffusion and osmosis
Identify examples of diffusion in plants, to include transpiration and gaseous exchange
To include:
OSMOSIS -
Is the movement of water from an area of low salt concentration to an area of relatively higher salt concentration through a semi permeable membrane
It is process by which roots absorb water
From soil. Osmosis also occurs in the movement of water within a plant and from cell to suave as water moving in to guard cells which then become turgid and open stomatal aperture
DIFFUSION
Is the movement of a gas or liquid from an area of high concentration to an area of relatively lower concentration of the gas and liquid.
Gaseous exchange:
molecules of oxygen and carbon dioxide diffuse in to the leaf via the stomata, oxygen diffuses in to the woody stems via lenticels
TRANSPIRATION
Water molecules diffuse from the leaf to the air during transpiration.
Identify examples of osmosis in plants
The cell wall is FULLY permeable I.e it allows both water & dissolved minerals to pass through
Cell wall Is SEMI permeable, allows water and only smallest particles to pass through.
This enables regulation of amount of water in cells
- the cell sap within the root cells contains a relatively high concentration of sugars and salts
- the soil water around the roots contains a relatively low concentration of solutes such as mineral salts
- the soil water (low concentration) will enter the root hairs (high concentration) through the elk membrane (semi permeable) by the process of Osmosis
Turgor
The cell vacuole will expand with the added water . The rigid cell wall resits the expansion of the vacuole and the cell becomes TURGID. It is this TURGOR which maintains the firm of all non woody plant structures
Cell expansion
If the cell is surrounded by a strong solution of sugars or salts, less water will enter the vacuole. The all pressure will fall and turgor is lost. The cell becomes FLACCID and the plant wilts. Cells will also become flaccid if there is no available water. Wilting is reversible by watering, if too late the cell structure can be damaged resulting in death of the cell or plant
Describe the pathway of water movement from the soil through the plant into the atmosphere
Soil water -
Plant absorbs water from soil through root hairs
Osmosis across root cells
Water moves across the root cortex cells in a controlled way by osmosis or in an uncontrolled mass flow through root cell walls. (endodermis)
When water reaches the endodermis, mass flow through the cell walls is stopped by the CASPARIAN strip in the endodermal cell walls and all of the water is directed through the endodermal cells which controls the water movement in to the xylem cells of the stele (vascular bundle)
Once in the xylem vessels of the stele, water is moved up the plant in 3 ways
1 - ROOT PRESSURE
movement of water up to a distance of 30cm by root pressure (osmotic forces)
2- CAPILLARY ACTION
water attraction to the sides of the xylem cells moves the water a few centimetres
3- TRANSPIRATION PULL
Is the major process where the water is drawn up the roots in to the stem and up to the leaves by a force created by transpiration. transpiration pull firms a continuous pipeline of water in the Xylem vessels from the roots to stems and leaves , known as the transpiration stream
xylem of stem (transpiration pull)
TranspirationI is the loss of water vapour from the leaves of the plant.
The greatest loss is via stomata , but also loss from the leaf lamina by evaporation from cell walls, although this is limited due to presence of waxy cuticle
Approx 98% of the water taken up by the roots moves through the plant and Is lost through transpiration
Water travels through the plant via the Xylem vessels, diffuses out of the Xylem and through the loosely packed cells of the spongy MESOPHYLL of the leaf. Water evaporates from the cell surfaces and leaves the plants through the stoma as water vapour.
State what is meant by the term ‘transpiration ‘
TranspirationI is the loss of water vapour from the leaves of the plant.
The greatest loss is via stomata , but also loss from the leaf lamina by evaporation from cell walls, although this is limited due to presence of waxy cuticle
Approx 98% of the water taken up by the roots moves through the plant and Is lost through transpiration
The amount of water lost from the leaves by transpiration will depend upon:
1- SOIL WATER AVAILABILITY
Low levels of soil water reduce transpiration; as the plant cannot replace water lost through the leaves, it wilts, resulting in closure of stomata. Plants do not transpire when the stomata are shut.
2- RELATIVE HUMIDITY
In high humidity, the air already holds a lot of water vapour so has less capacity to absorb more water, therefore there is less evaporation from the stomatal aperture if atmospheric humidity is high.
3- AIR TEMPERATURE
Warm air can hold more moisture than cool air, so higher temperatures mean greater transpiration from the plant
4- WIND SPEED
Humid air close to the stomata will be dispersed in windy weather and replaced with less humid air, stimulating higher levels of evaporation from the stomata and therefore increasing the transpiration rate. Still conditions will reduce transpiration as humid air remains close to the stomata
5- LIGHT LEVELS
Stomata open in light and close in darkness.
Consequently transpiration rates are higher during the day
List factors that effect the rate of transpiration, relative humidity
Temperature, wind speed
Describe how the plant may limit water loss
Need 1 plant example for each adaption
To include:
Stomatal closure and leaf adaptions (hairs, think cuticle, needles)
PLANT ADAPTIONS
STOMATAL CLOSURE
A Stoma consist of 2 guard cells that surround the stomatal aperture. The guard cells are responsible for the opening and closing of the stomatal aperture. The inner walls of the guard cells are thickened . When the cell takes up water the cell walls expand unevenly and the thickened inner walls are pulled apart to create an aperture.
If the guard cells become flaccid the stomatal aperture closes. Plants will also close their stomata when the plant looses turgidity. This will occur when the plant is lacking water or the rate of transpiration exceeds water intake .
ROLLED LEAVES
Some plants eg pines and grasses have rolled leaves which greatly reduce the exposed surface area of the leaves and cuts down transpiration, both these plants are adapted for costal environments
Ex: Festuca glauca
THICKENED CUTICLE
leaves May have a thick waxy cuticle over the leaf surface, eg many evergreens, this reduces water loss through cell walls by evaporation rather than through stomata
Ex: Ilex aquifolium
SUNKEN STOMATA
in some places the stomata are found in slight depressions below the leafs surface, this helps to create a moist atmosphere around the stomata
Ex: Pinus sylvestris (Scots pine)
HAIRY LEAVES
Hairs on leaves trap moisture near the surface, creating a humid environment close to the leads surface. Hair also reflect light, reducing temperatures near the leaf
Ex: Stachys byzantina (lambs ear)
SILVER LEAVES
Silver leaves reflect light, which reduces temperature, eg:
Lavandula angustifolia (lavender)
REDUCED LEAVES
Small or thin leaves, sometimes reduced to only spines, as in some cacti , are effective in reducing transpiration loss
Opuntia polycantha (prickly pear)
H
Describe the uptake and distribution of mineral nutrients in the plant
PLANT MINERAL NUTRIENT UPTAKE
- plants absorb mineral nutrients (ions) ie, NITRATE, PHOSPHATE & POTASSIUM in a soluble form.
- minerals are dissolved on water in the soil & absorbed by root hairs - process called ACTIVE TRANSPORT
- root hairs have carrier molecules on their cell membranes, these pick up the mineral ions and move them across the membrane into the cell against the concentration gradient.
- usually substances move down a concentration gradient in diffusion,so active transport is quite different
- active transport needs energy from respiration to move the ions across the root hair cell membrane and in to the plant.
- these mineral nutrients are then transported around the plant in the vascular tissue - Xylem and Phloem
Nutrients from soil solution active uptake against concentration gradient into root cells.
Transport through the plant in xylem
Distribution through the phloem
Identify examples of diffusion In plants
Transpiration
Water molecules diffuse from the leaf to the air during transpiration
Gaseous exchange
Molecules of oxygen and carbon dioxide diffuse in to the leaf via the stomata. Oxygen diffuses in to woody stems via lenticels.
List horticultural operations to reduce transpiration
SHADING
Reduces transpiration
Lowers temp in greenhouse - reduces amount of water vapour the air can contain.
- shade with shade paint, blinds, green netting
MISTING
- overhead watering keeps atmosphere humid-reduces water vapour drawn from plant
- evaporation causes cooling, reducing temps overall
WIND BREAKS
- Transpiration increases in windy weather
- reduce wind = reduce transpiration (by use of hedges, shelter belts, wind filtering mesh& fencing)
VENTILATION
- reduces temperature- reduces amount of water vapour in Air
- ventilation also reduces humidity - increases transpiration (be careful)
ANTI - TRANSPARENT SPRAYS
- applied to foliage - blocks stomata- reduces transpiration
- commonly used on Xmas trees - or bare root evergreen plants before lifting and transplanting
- blocked stomata = Reduced rate of photosynthesis
Describe PLASMOLYSED CELL
PLASMOLYSIS
If cell placed in strong solution , water pass from cell vacuole into the stronger solution
This causes vacuole and cytoplasm to contract away from the cell walll and become PLASMOLYSED, damaging the plasmodesmata
PLASMOLYSED CELL
PLASMOLYSIS does not normally occur naturally. As the soil water surrounding the roots is normally of s weaker solution they the cell sap, and water moves out of the root cells into the soil causing PLASMOLYSIS
CONDITIONS THST LEAD TO THIS OCCURING
- excessive high levels of fertiliser being added to the soil
- SALTING OF ROADS CONTAMINATING SOIL
- Flooding by sea
