Plant Classification, Photosynthesis
and Plant Reproduction
(Worksheet 2)
Photosynthesis
Photosynthesis is a chemical reaction that plants use to make their food
(glucose) using energy from the sun. Photosynthesis occurs within the leaves.
The leaves then use the glucose to generate other useful substances and to
obtain energy through respiration. Photosynthesis only occurs in the light.
The word equation for Photosynthesis is:
| Light and chlorophyll | ||
| Carbon Dioxide + Water | ----------------------------> | Glucose + Oxygen |
The balanced chemical equation is: 6CO2
+ 6H2O --> C6H12O6 + 6O2
**Make sure you learn both these equations - it is highly likely that you will be asked these in your exam**
The Process of Photosynthesis
Read the following passage carefully. There will be questions at the end for you
to answer.
The process of photosynthesis takes place in the leaves. This means that all the
different components of the chemical reaction must be present within the leaves
for Photosynthesis to occur. Carbon Dioxide enters the leaf through tiny holes
on the under surface of the leaf. These holes are called stomata.
Chloroplasts containing chlorophyll occur in their greatest numbers on the upper side of the leaf in palisade cells. The chlorophyll is a green pigment that absorbs the energy from sunlight so that photosynthesis can take place.
Inside the leaf there are veins that are continuous extensions of the stems and roots. These veins contain xylem and phloem, two types of plant tissue that transport certain substances throughout the plant. The xylem transports water to the leaves from the roots since water is needed for photosynthesis to occur.
The phloem transports glucose (created by photosynthesis) away from the leaves and around the plant to where the glucose is most needed. This tends to be the growing areas (the buds) and the storage areas (the roots).
The oxygen that is produced as a result of
photosynthesis leaves the plant through the stomata through the process of
diffusion.
The rate of photosynthesis can be affected by the availability of certain key
components. For example if there is more light then the rate of photosynthesis
will increase. The same is true if there is a greater concentration of carbon
dioxide.
Temperature also affects the rate of photosynthesis - the optimum temperature for photosynthesis to occur is 30 degrees centigrade. If the temperature is greater than 45 degrees centigrade the rate of photosynthesis will slow down.
Answer the following:
1) In which part of the plant does photosynthesis occur?
2) What four components do you need for photosynthesis to occur?
3) What are stomata?
4) How is oxygen removed from the plant?
5) What does the xylem transport?
6) Name two key areas where glucose is transported to.
7) What plant tissue is responsible for transporting the glucose around the plant?
8) Name two factors that can lead to a change in rate of photosynthesis.
9) Chloroplasts are present in which cells on the upper side of leaves?
10) Which component absorbs the energy
from sunlight for photosynthesis to occur?
Chlorophyll.