Photosynthesis and leaf structure Flashcards
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
Photosynthesis Equation
Carbon Dioxide+Water->Glucose+Oxygen
Chlorophyll
Chlorophyll is a green pigment that is found in chloroplasts within plant cells
It is this pigment which gives plants their characteristic green colour Chlorophyll transfers energy from light into energy in chemicals, for the synthesis of carbohydrates
It is essential for photosynthesis to occur
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
Minerals in Plants
Photosynthesis produces carbohydrates, but plants contain many other types of biological molecule; such as proteins, lipids and nucleic acid (DNA)
As plants do not eat, they need to make these substances themselves
Carbohydrates contain the elements carbon, hydrogen and oxygen but proteins, for example, contain nitrogen as well (and certain amino acids contain other elements too)
Other chemicals in plants contain different elements as well, for example chlorophyll contains magnesium and nitrogen
This means that without a source of these elements, plants cannot photosynthesise or grow properly
Plants obtain these elements in the form of mineral ions actively absorbed from the soil by root hair cells
‘Mineral’ is a term used to describe any naturally occurring inorganic substance
Investigating the Need for Chlorophyll
A leaf is dropped in boiling water to kill the cells and break down the cell membranes
The leaf is left for 5-10 minutes in hot ethanol in a boiling tube. This removes the chlorophyll so colour changes from iodine can be seen more clearly
The leaf is dipped in boiling water to soften it
The leaf is spread out on a white tile and covered with iodine solution
In a green leaf, the entire leaf will turn blue-black as photosynthesis is occurring in all areas of the leaf
This method can also be used to test whether chlorophyll is needed for photosynthesis by using a variegated leaf (one that is partially green and partially white)
The white areas of the leaf contain no chlorophyll and when the leaf is tested only the areas that contain chlorophyll stain blue-black
The areas that had no chlorophyll remain orange-brown as no photosynthesis is occurring here and so no starch is stored
Investigating the rate of photosynthesis
As photosynthesis occurs, oxygen gas produced is released
As the plant is in water, the oxygen released can be seen as bubbles leaving the cut end of the pondweed
The number of bubbles produced over a minute can be counted to record the rate
The more bubbles produced per minute, the faster the rate of photosynthesis
A more accurate version of this experiment is to collect the oxygen released in a test tube inverted over the top of the pond weed over a longer period of time and then measure the volume of oxygen collected
Investigating Gas exchange
Plants are respiring all the time and so plant cells are taking in oxygen and releasing carbon dioxide as a result of aerobic respiration
Plants also photosynthesise during daylight hours, for which they need to take in carbon dioxide and release the oxygen made in photosynthesis
At night, plants do not photosynthesise but they continue to respire, meaning they take in oxygen and give out carbon dioxide
Photosynthesis Equation Extended
6CO2+6H2O->C6H12O6+6O2
Limiting factors
Temperature
Light intensity
Carbon dioxide concentration
Leaf structure
Wax Cuticle
Upper Epirdermis
Palisade Mesophyll
Spongy Mesophyll
