Plant Cells

Introduction to Plant Cells

  • Plant cells are the basic unit of life in plants and share some common features with animal cells.
  • However, in addition to the common cell components, they have some special structures like the cell wall, chloroplasts and a large central vacuole.

Parts of a Plant Cell

  • The cell wall surrounds the cell membrane, providing rigidity, support and protection against mechanical stress and pathogens. It is primarily made up of the carbohydrate cellulose.
  • The cell membrane controls the movement of substances in and out of the cell.
  • The cytoplasm is a gel-like substance where many of the cell’s metabolic processes occur.
  • The nucleus contains DNA, the genetic material of the cell, and controls the cell’s activities.
  • The chloroplasts are the site of photosynthesis. They contain chlorophyll, a pigment that captures light energy to convert water and carbon dioxide into glucose.
  • The large central vacuole stores water, nutrients and waste products, helping to maintain turgor pressure against the cell wall which gives the plant its rigid structure.
  • The mitochondria are the powerhouse of the cell, releasing energy from glucose during the process of respiration.
  • The ribosomes are small particles where proteins are made according to the cell’s requirements.
  • The endoplasmic reticulum is involved in the production and transport of proteins and lipids.

Differences between Plant and Animal Cells

  • Unlike animal cells, plant cells have a rigid cell wall which gives structure to the plant and protects the cell.
  • Plant cells have chloroplasts where photosynthesis occurs to produce food. Animal cells don’t have chloroplasts as they don’t photosynthesize.
  • Plant cells usually have a large, single central vacuole that maintains cell turgidity, whereas animal cells may have smaller vacuoles.

Cell Specialisation in Plants

  • Some plant cells are specialised to perform specific functions. For example:
    • Root hair cells have a large surface area to absorb water and minerals from the soil.
    • Guard cells control the size of the stomata on the surface of leaves to manage gas exchange and water loss.
    • Xylem cells are dead cells which form a hollow tube for transporting water and dissolved minerals from roots to other parts of the plant.
    • Phloem cells transport sugars and other soluble substances throughout the plant.

Photosynthesis

  • Photosynthesis is an essential process that occurs in the chloroplasts of plant cells, where light energy is converted into chemical energy in the form of glucose.
  • The general equation for photosynthesis is: 6CO2 + 6H2O → C6H12O6 + 6O2 (carbon dioxide + water → glucose + oxygen)

Examining Cells under a Microscope

  • Plant cells can be observed under a microscope by performing a simple experiment with onion cells or leaf cells:
    • Firstly, a thin layer of cells is peeled off and placed on a slide.
    • A staining agent like iodine can be used to highlight certain cell structures.
    • The cover slip is carefully placed over the cells and examined under the microscope.