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    This module is included inLens: Siyavula: Natural Sciences (Gr. 7-9)
    By: Siyavula

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Structure of a plant cell

Module by: Siyavula Uploaders. E-mail the author

NATURAL SCIENCES

Grade 9

PLANTS: STRUCTURE, INCLUDING GENETICS

Module 26

STRUCTURE OF A PLANT CELL

Activity:

To understand the structure of a plant cell

[LO 2.1, 2.2, 2.3, 2.4]

Ask your educator for a leaf from a moss plant, or some other example, to study through a microscope.

You could study the structure of a typical leaf. The following illustration is a simple line drawing providing a two-dimensional image of what you might see:

The cell consists of a framework filled with a special liquid – PROTOPLASM – with a variety of structures floating in it. Some of these are too small to be seen through an ordinary microscope. We need to use an electron microscope to examine these small structures. Remember that you see the cell from one side only. It is actually shaped like a brick and we say that it is three-dimensional. Ask your educator to explain this concept to you.

Find out about microscopes and electron microscopes.

Figure 1
Figure 1 (graphics1.png)

Assignment 1:

1. Provide a caption for the sketch.

2. Add labels in the numbered boxes.

3. What are the functions of each?

Table 1
LabelNumber Labels
1.  
2.  
3.  
4.  
5.  
6.  
7.  
8.  

Assignment 2: The nucleus contains fine details that you need to get to know before working through the rest of the module:

Figure 2
Figure 2 (graphics2.png)

Discuss each of the labels of the nucleus in class and summarise their functions.

Table 2
  Label
1. Nucleole
2. Chromatin network
3. Nuclear membrane
4. Nucleoplasm

Can you remember the main function of the nucleus?

Although the nucleus is the control centre of the cell, there are two other organelles that require closer investigation because of the important functions that they perform.

Plants engage in PHOTOSYNTHESIS and RESPIRATION. The organelles that are involved in this are the CHLOROPLAST (photosynthesis) and the MITOCHONDRION (respiration). You will be learning more about these organelles in future.

Your educator will show detailed sketches of these organelles to introduce them in greater detail.

Assessment: The identification of cellular structure

Were you able to distinguish the basic structures?

[ LO 2.1; LO 2.3]

Assignment 3:

Make simple line drawings of the organelles,

Which of the structures and aspects that form part of the plant cell would you not expect to come across in an animal cell? Supply reasons:

(Suggestion: Look at yourself and at a plant, and feel what you are like and what a plant is like.)

Assessment: Line drawings and deductions

Were you able to do the sketches and make deductions? [LO 2.3; LO 2.4]

By now, you probably understand that plant cells have particular characteristics but that they do not all look the same, because they are adapted to fulfil specific functions. These adaptations in their structure are referred to as DIFFERENTIATION and the accompanying change of function is known as SPECIALISATION. Both terms are important in cellular studies.

A group of cells that are adapted to perform a particular function is called a particular kind of TISSUE. Some conduct water through the plant. Other groups of cells are responsible for strengthening the plant. More, still, are adapted for photosynthesis.

Tissues are grouped together to perform a combined function. Such a structure, consisting of many different kinds of plant tissue, but with a combined main function, is known as an ORGAN, e.g. a leaf.

Assessment

LO 1: Scientific investigations:

The learner will be able to act confidently on curiosity about natural phenomena, and to investigate relationships and solve problems in scientific, technological and environmental contexts.

This is evident when the learner:

  • conducts investigations and collects data;
  • evaluates data and communicates findings.

LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

  • recalls meaningful information;
  • categorises information;
  • interprets information;

2.4 applies knowledge.

Memorandum

PLANT CELL

  • It consists of a framework containing a special liquid – PROTOPLASM –with a variety of structures suspended in it.

Assignment 3

  • Control the light quantity carefully with the condensor/
  • Focus carefully up and down when busy with the maximum enlargement.
  • Colouring: with iodine solution for better self definition starch grains will also colour.

Activity

Assignment 1

  1. Sketch of the plant cell:
Figure 3
Figure 3 (graphics3.png)
Table 3
LabelNumber Function
1. Photosynthesis occurs here
2. Controls all cell activity
3. Membrane enclosing the vacuole; vacuole stores moisture and colourants
4. Moisture, colourants
5. Respiration, produces energy
6. External protective and strengthening membrane
7. Controls entry and exit of substances
8. Medium in which reactions occur and in which the organelles are suspended

Assignment 2:

THE NUCLEUS

Figure 4
Figure 4 (graphics4.png)

Table 4
  Function
1. Controls molecules in the nucleus
2. Stores genetic material; bears heriditary characteristics
3. Contains nuclear material, communicates with the rest of the cell
4. Special structures and moisture

Assignment 3

  • Plants PHOTOSYNTHESISE and RESPIRE. The two organelles that are involved are the CHLOROPLAST and the MITOCHONDRION.
  • Studying this aspect of natural science remains important right through to matric.

CHLOROPLASTS

Contain the colour pigment chlorophyll;

Accommodate photosynthesis;

Enclosed by a double membrane;

Contains stroma of liquid and grana – stacked hollow disks (thylacoids) that are suspended in it. Grana are attached to other flat membranes (lamellae).

MITOCHONDRIA

accommodate the ENERGY-providing process of RESPIRATION;

also enclosed by a double membrane;

a fold/ridge of the inner membrane is called a crista (cristae);

the matrix is the liquid inside the mitochondrion.

  • All the organelles that might occur are not discussed in Grade 9, but those that are mentioned will indicate some of the differences between typical plant and typical animal cells.
Table 5
Explanation
Absent in animal cells; maintans form and provides sturdiness in plant cells, as plants have no supporting skeletons.
Small or absent in the case of animal cells; it provides storage and also adds to the sturdiness of the plant cell.
Animal cells have no PLASTIDS.
Plant cells have a fixed shape determined by the cell wall – animal cells come in many shapes.
  • Perhaps you have realised that plant cells are unique. In nature, though, there is endless variation in the shape and characteristics of plant cells. Such variation of form is referred to as DIFFERENTIATION, the variation in function that accompanies it is referred to as SPECIALISATION. Both of these terms are of importance in the biological study of cells.
  • When cells are grouped together, we have to do with the next level of organisation, namely TISSUES. Tissuea are cells that are grouped together to execute a specific task.
  • This, for example, provides for cells that only serve to conduct water through the plant – the xylem.
  • Tissues are also grouped together to perform a combined function. Such a structure, consisting of many different kinds of plant tissue, but with a combined main function, is known as an ORGAN.

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