6. Plant nutrition Flashcards
Photosynthesis
The chemical process by which plants manufacture carbohydrates from raw materials using energy from light.
Carbon dioxide + Water –> Glucose + Oxygen
Products needed for photosynthesis
- Carbon dioxide
- Water
- Chlorophyll
- Chloroplasts
- Sunlight
Balanced equation for photosynthesis
6CO² + 6H²O —> C⁶H¹²O⁶ + 6O²
Chlorophyll
Green pigment found in plants, which absorbs energy from sunlight for photosynthesis.
Chloroplasts
Sub-cellular structures found in some plant cells; the site of photosynthesis.
Use of glucose in plants
Glucose is a source of chemical energy.
Some of the glucose produced by photosynthesis is broken down during respiration to release energy.
Photosynthesis - Use of carbohydrates as storage
Glucose = highly reactive molecule –> unwanted chemical reactions may happen.
- Glucose converted into sucrose (more stable molecule) before being transported in the phloem to the different parts of the plant
- Sucrose can easily be changed back to glucose when needed by the plant.
- Convert glucose to starch (stored in granules in the chloroplasts + cytoplasm and acts as an energy store) (stored in leaves) –> starch used bc it is insoluble (won’t be affected by movement of water) –> used as longterm energy source
- Starch can be converted back into glucose for respiration.
Use of carbohydrates for structural support
Some glucose is converted to cellulose. Cellulose is an important component of the plant cell walls.
Cellulose
A complex carbohydrate that forms tough fibres, which are the main constituent of plant cell walls.
Photosynthesis - Use of carbohydrates in pollination
- Glucose is also used to make nectar.
- Nectar is a sweet, sugary liquid that attracts animals like insects and birds.
- These animals in turn help with pollination.
Use of sucrose in plants
- Sucrose is transported through the phloem.
- Sucrose is used for the growth of shoots and young leaves.
- Sucrose is used for the growth of the roots or converted to starch and stored.
- Sucrose is used for the growth of the fruit or stored in the fruit.
Minerals
A group of substances that are essential to organisms in low concentrations to allow them to carry out various functions.
- Inorganic substances such as magnesium nitrate
- Formed in the soil by natural breakdown of rocks.
- Many minerals are insoluble in water. But those that are soluble can be used by plants.
- Theres minerals break down into their ions (mineral ions) and can be absorbed by root hair cells in plant roots.
Use of mineral ions
- Plants use magnesium ions for making chlorophyll.
- There is a magnesium ion at the centre of each chlorophyll molecule, and this is vital for the correct function of chlorophyll.
- Plants use nitrate ions for making amino acids.
- Amino acids are used by the plant to make the proteins it needs.
Limiting factor
The variable in the environment that controls the rate, growth or abundance of a biological processes. For instance, temperature can be the limiting factor in the growth of a plant.
When a process depends on two or more factors, the rate of that process is limited by the factor which is in shortest supply.
Examples of limiting factors of growth of plants
Light intensity, availability of carbon dioxide, temperature (bc enzymes breaking down carbon dioxide + water need optimum temp)
Water/ions + chlorophylls → they are limiting factors just more difficult to measure.
Graph of one limiting factor on a graph.
eg. carbon dioxide.
As the amount of carbon dioxide increases, so does the rate of reaction. Eventually though the line plateau’s.
This happens when carbon dioxide has increased in supply to the point where it is no longer the limiting factor (eg. instead sunlight is)
Waxy cuticle
Function
- Stops water from evaporating from the leaf
Adaptation
- Waxy layer
Chloroplast
Function
- The site of photosynthesis
Adaptation
- Contains chlorophyll to absorb light, and enzymes and structures needed for photosynthesis
Upper epidermis
Function
- Protects the inner cells
Adaptation
- Thin layer without chloroplasts, which lets light pass through for photosynthesis
Palisade mesophyll layer
Function
- Tissue in which photosynthesis happens
Adaptation
- Box-shaped cells that pack closely together; each cell has lots of chloroplasts pushed to the edges of the cell by a large vacuole so they can absorb more light
(Close to the surface of the leaf)
Xylem
Function
- Carries water and mineral ions from the roots to the leaf
Adaptation
- Made from dead cells, forming hollow, waterproof tubes, through which water passes
Phloem
Function
- Carries sucrose away from the leaf
Adaptation
- Consists of sieve tubes (through which the sucrose is transported) and companion cells (that provide energy for the transport)
Vascular bundle
Function
- Contain the xylem and phloem tissues
Lower epidermis
Function
- Protects the inner cells
Adaptation
- Thin layer that (apart from guard cells) does not contain chloroplasts, which lets light pass through for photosynthesis
Guard cells
Function
- Work in pairs to control the size of the opening of a stoma
Adaptation
- Entry and loss of water from the guard cells (due to osmosis) results in changes in their shape; this in turn leads to the opening and closing of the stoma
Stomata
Function
- Controls the diffusion of water vapour and gases in and out of the leaf
Adaptation
- The size of the opening changes in response to the internal and external environments of the plant
Air spaces
Function
- Allow diffusion of gases throughout the leaf
