Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.
|Green plants are extremely significant because they are the only organisms with the biochemical ability to "make" chemically complex organic food for themselves, starting with simple inorganic substances.|
|The process is called photosynthesis, and it uses the energy of light. Some of the sun's light energy is absorbed by the quite remarkable green pigment chlorophyll, and converted into chemical energy, stored in the molecular structure of the sugars and other compounds derived from them.|
| In the process, green plants use
up carbon dioxide and produce oxygen, which is needed by most living
organisms especially animals for respiration . Green plants
therefore have a major impact on the air around us, and in fact on the
In addition, all animals depend on plants for their supply of food. All the major components of diet are synthesised by plants in the first place.
Why are 2 words written above the arrow?
> they are not reactants or products - essential but chlorophyll is not used up
What are the similarities and differences between the (word) equations for photosynthesis and aerobic respiration?
>same substances, different direction (respiration needs no light/chlorophyll)
What are the main parts of a plant where photosynthesis takes place?
What does the word photosynthesis mean?
> putting together with light
Where is the chlorophyll? Be as specific as possible.
> inside chloroplasts inside mesophyll cells of leaf
What happens to photosynthesis at night?
> it stops
Taking each of the 4 main ways that plants use glucose from photosynthesis in turn, say whether this could be passed on to you if you were to eat the plant. Explain why, and answer the supplementary question in each case.
|Use to which plant put glucose||Possible use to Man when plant is eaten?|
|1 (gives plant energy)||no - already used up|
|2 (stored for later use)||yes - roots/seeds/fruits are edible|
|3 (converted into cellulose)||no - forms indigestible fibre|
|4 (used for synthesis of proteins)||yes - digested back into amino acids|
By what process does the plant obtain energy? > respiration
In what chemical form is glucose/food stored for later use?> starch/oil
For what purpose is glucose converted into cellulose? > cell walls
By the addition of which element can carbohydrates such as glucose be used for the synthesis of proteins?> nitrogen
carbon dioxide concentration > proportionate increase in photosynthesis
light intensity > proportionate increase in photosynthesis up to plateau
temperature > proportionate increase in photosynthesis in certain range
Which of these would be a limiting factor in a normal warm day?
> carbon dioxide concentration
The principles of manipulating the previously mentioned factors required for photosynthesis can be used in order to provide optimum conditions for plant growth in glasshouses, and in an ecological context to improve the efficiency of energy tranfer in the production of food. For instance, with some crops, horticulturists find it is worthwhile installing gas heating, and releasing the exhaust gases directly into the glasshouses where they grow. Give a logical chain of explanation for this finding.
> Extra warmth speeds up metabolism, and the extra carbon dioxide results in extra photosynthesis, extra food, extra growth, extra yield, extra PROFIT!
> This allows more light (and
water etc?) to reach the grass plants below
Some gardeners like to grow varieties of plants with leaves which are not as green as the usual plant,e.g. "golden" privet.
Why do they sometimes find that these plants are overtaken by green sections?
> Greener plants grow more efficiently
This food produced by plants is the same sort of food which we might eat (carbohydrates, fats, proteins, etc.).
See the side panel of the Cornflakes packet (data from an old packet - modern data values differ slightly in detail), and answer the questions below.
Refer to the units on the respiration process to see what might happen to it!
What biological justification is there for the claim that this breakfast cereal has a link with sunshine?
> the corn plant makes food by
|For 30g Serving with
(of which sugars) g
(of which saturates) g
VITAMIN D µg
THIAMIN (B1) mg
RIBOFLAVIN (B2) mg
VITAMIN B6 mg
FOLIC ACID µg
VITAMIN B12 µg
|IRON mg||7.9 (55)||2.4 (17)|
> starch > 75%
In fact the main inorganic nutrients used by plants are carbon dioxide gas from air (how much in the atmosphere? > 0.04 %) and waterfrom soil.
The distinction between organic and inorganic compounds is so important that it is worthwhile sorting some substances into groups, with formulae if possible:
( List of examples: carbon dioxide, glucose, nitrate ion, oxygen, protein, starch, water - add more if you can)
Virtually all other forms of life - including Man - depend on plants for these complex organic substances, either as building blocks for their growth, or as fuel - recovering the energy taken from the sun in the first place. As such they are hijacking the products of plants" activities!
It is a curious fact that oxygen is produced by green plants as a waste by- product of the process, and because not much of it is needed by plants, they release it into the atmosphere!
What is this process (getting rid of waste) called?
What process in living organisms uses up oxygen? (2 words)
> aerobic respiration
What sort of organisms carry out this process?
> almost all
What is the general name for the process which uses up oxygen, not in living organisms?