4.3 Movement of water and minerals Flashcards
Definition of diffusion
Movement of particles from an area of high concentration to an area of low concentration.
Definition of osmosis
The method by which water enters cells.
Movement of water from a high water (low solute) concentration to a low water (high solute) concentration across a selectively permeable membrane.
Where does diffusion happen in a plant?
In the spaces between the cells
Through the cell walls
Where does osmosis happen in a plant?
Through cell membranes
Example of diffusion in a plant:
Movement of gases such as carbon dioxide into and water vapour & oxygen out of a leaf through the stomata (as in PHOTOSYNTHESIS & RESPIRATION)
TWO examples of osmosis in a plant:
- To increase turgor pressure, water will move across a selectively permeable cell membrane into a cell’s vacuole to increase this pressure;
- Water is drawn into root hair cells from the soil when there is a higher concentration of water in the soil than in the roots.
Describe pathway of water from soil through plant into atmosphere:
Water enters root hairs by osmosis, and diffuses between cells or through cells, passing through cells in the endodermis;
Water reaches the xylem of the root and is sucked up like a straw by evaporation from leaves above (transpirational pull);
Water enters leaves through xylem in veins, travels across leaf cells by osmosis, and flows through leaf cell walls;
Water evaporates from leaf cell walls into mesophyll spaces;
Water vapour then diffuses through stomata of a leaf.
What factors affect the rate of transpiration? (4)
Humidity - decreases transpiration rate
Wind speed - dry windy conditions will reduce humidity and increase transpiration.
Temperature - as temperature rises, transpiration will increase. However, at very high temperatures, stomata will close and transpiration will cease
Light intensity affects rate due to response of stomata to light levels (they generally close at night to reduce water loss)
How may a plant limit water loss?
By closing the stomata;
By using leaf adaptations, such as:
- hairs
- thick cuticle
- needles
- waxy leaves
Describe the uptake and distribution of mineral nutrients in a plant in the cases of:
(1) Root Hair Cells, (2) Xylem, (3) Phloem
(1) Root hair cells take in nutrients from the soil. Their concentration are often higher inside the root hair cell than in the soil, so they are trying to pass against the concentration gradient. But active transport will allow the nutrients to enter the cells (using the energy from respiration)
(2) Mineral nutrients are transported from the roots UP through the xylem to the leaves and also other parts of the plant
(3) Phloem tissues transport sugars (food) made in photosynthesis from the leaves, UP and DOWN the plant, to other plant organs, where is it used in respiration to release energy or is stored as starch for later use.
Describe active transport and the reason for it:
The selective uptake of nutrients across cell membrane against their concentration gradient (or UP a concentration gradient)
Nutrients cannot enter cells by passive diffusion as the concentration of nutrients inside cells is greater than the concentration in the soil water: uptake is AGAINST a concentration gradient.
Nutrients therefore have to be taken in by a process called Active Transport, which requires energy (released during respiration)
How are the internal and external structure of the (dicot) leaf designed to maximise photosynthesis AND minimise transpiration. (In other words, how are plants adapted to do both things at the same time)?
The cuticle (external) will prevent water loss (minimising transpiration) BUT it is thin enough to allow light through to the palisade mesophyll cell layer (internal) so photosynthesis can take place.
State FOUR functions of water in a plant
Creates turgor which enables cell expansion
Supports herbaceous plants
Used in photosynthesis
Essential in triggering germination
Describe the pathway of water through the stems
Water moves through the xylem in upwards direction only by transpirational pull.
This can be through adhesion of water molecules to xylem vessel wall.
Describe the pathway of water through the leaves to the air
Water enters a leaf through xylem in leaf veins, travels across and throughout leaf cells by osmosis, and flows through leaf cell walls;
Water evaporates in the spongy mesophyll and into the air spaces;
If the stomata are open, water diffuses through them as water vapour (transpiration), and into the air.
