Page 10 - Biology - XII

SECTION - A

Plant Population Density
1 Plant Population Density
and Isolation of
and Isolation of DNADNA

EXPERIMENT - 1

Objective
To study the plant population density by quadrat method.

Principle/Theory
Density is defi ned as the numerical strength. In
case of plant, population density is the numerical
strength of a certain plant species in the plant
community per unit area at a given time. Thus, the
number of individuals of any species in any unit
area at a given time is its density.

Note: The unit area may be 5 sq. cm (small) or
10 sq. metre (large) depending upon the Fig. 1.1: Grass fi eld with a variety of plants
nature of the plant community you want to study.
Normally, 1 sq. metre unit area is used for study of a herbaceous vegetation. Density which gives an idea
of the degree of competition is calculated by:

Density = Total number of individuals of the species in all ssampling units
Total number of sampling units studied
The value thus obtained is expressed as number of individuals per unit area. Quadrat is a square unit area.
Plant population density can be studied by using Quadrat method.

Materials Required 100 cm Nail String Quadrat Size 1 m × 1 m
Meter scale, string, nails, hammer, measuring tape, 90 cm Nail
and note pad/paper
80 cm

Procedure 70 cm String
1. Select a wildly growing fi eld/ground/park/or 60 cm
grassland near your school. 50 cm
2. Fix a nail on the ground in the area you have 40 cm Quadrat Size
selected. 30 cm 50 cm × 50 cm
3. To make a L-shaped structure, fi x two more 20 cm
nails on either sides of the fi rst nail. 10 cm
4. From the two arms of L-shaped structure,
measure 10 cm. Now, fi x the nails and string. 0 10 20 30 40 50 60 70 80 90 100 cm
This gives you an area of 10 cm × 10 cm. This (1 m)
gives the fi rst quadrat for study. Plant species 1 Plant species 2 Plant species 3
Fig. 1.2: Making of quadrats in a grassland/grass fi eld

9