Plant Nutrition Flashcards
Define Photosynthesis
Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water
At the same time oxygen is made and released as a waste product
The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun
So photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light
Define Chlorophyll
Chlorophyll is a green pigment that is found in chloroplasts within plant cells
It reflects green light, giving plants their characteristic green colour
Chlorophyll absorbs light energy; its role is to transfer energy from light into energy in chemicals, for the synthesis of carbohydrates, such as glucose
Photosynthesis will not occur in the absence of chlorophyll
Use & Storage of Carbohydrates
Converted into starch molecules which act as an effective energy store
Converted into cellulose to build cell walls
Glucose can be used in respiration to provide energy
Converted to sucrose for transport in the phloem
As nectar to attract insects for pollination
limiting factor Temperature
As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes
However, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature beyond which the enzymes begin to denature and the rate of reaction decreases
limiting factor Sunlight
The more light a plant receives, the faster the rate of photosynthesis
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
At low light intensities, increasing the intensity will initially increase the rate of photosynthesis. At a certain point, increasing the light intensity stops increasing the rate. The rate becomes constant regardless of how much light intensity increases as something else is limiting the rate
The factors which could be limiting the rate when the line on the graph is horizontal include temperature not being high enough or not enough carbon dioxide.
Limiting factor Carbon dioxide concentration
Carbon dioxide is one of the raw materials required for photosynthesis
This means the more carbon dioxide that is present, the faster the reaction can occur
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
Describe the upper epidermis layer
On the top of the leaf is the upper epidermis. The cells in this layer are packed tightly together, to reduce the quanitity of water vapour escaping the leaf. They do not contain chloroplasts, So they cannot photoysnthesise. These cells secrete mucus a waxy substance which forms a thin, transparent, waterproof covering called cuticle.
Describe the Palisade Mesophyll layer
Palisade mesophyll layer is made of tall narrow cells containing very large number of chloroplasts. Their main function is photosynthesis. As they are close to the top of the leaf, they get plenty of sunlight. The transparent epidermis cells above them let the sunlight through easily.
Describe the Spongy Mesophyll cell
The cells in this tissue contain chloroplasts, but not as many as palisade cells. They are not as tightly packed either. There are many air spaces between them. These spaces allows carbon dioxide and oxygen to diffuse between the air and the cells inside the leaf. These spaces also allow vapour to move from the surface of the cells to the outside the leaf.
Describe the lower epidermis cell
There are openings in the lower stomata. Each stomata is surrounded by a pair of guard cells, unlike the other cells in the epidermis, contain chloroplasts. The guard cells can change shape, which can open and close the stomata. The stomata allow diffusion of carbon dioxde and oxygen in and out of the leaf. Water vapour also diffuses out of the leaf through the stomata
