Comprehensive Notes on Cell Structure and Organisation

Cell Structure and Organisation

What Are Cells?

• Cells are the basic building blocks of life, functioning as chemical factories that perform various tasks to keep organisms alive.

• A cell takes in raw materials, converts them into new molecules through chemical reactions, and uses these molecules to perform different functions.

How Did Cells Get Their Name?

• Robert Hooke coined the term 'cells' in 1667.

• Hooke used early microscopes to examine thin slices of tree bark.

• He observed packed, small boxes with thick walls, resembling cells in a prison, hence the name.

How Can We Study the Parts of the Cell?

• Most cells are too small to be seen without assistance.

• Light microscopes (1000x magnification) and electron microscopes (200,000x magnification) are used to view cells and their parts.

• Robert Hooke and Anton van Leeuwenhoek were inventors of microscopes.

• Cameras can be attached to microscopes to capture images called micrographs.

Viewing Cells from Different Perspectives

• It's important to view cells from different perspectives by cutting them along their length and at right angles to their length.

Cell Composition

• A cell consists of protoplasm, which is the living matter.

• Protoplasm is made up of three parts: cytoplasm, nucleus, and cell membrane.

Cell Membrane

• The cell membrane surrounds the cytoplasm.

• It is composed of lipids (lipid bilayer) and proteins.

• It is partially permeable, allowing only small and soluble substances to pass through.

Cell Wall

• Plant cells have a cell wall surrounding the cell membrane.

• The cell wall is made of cellulose.

• It is fully permeable.

• It protects the cell from injury and provides a fixed shape.

Cytoplasm

• The cytoplasm is located between the cell membrane and the nucleus.

• It is the site of cellular activities.

• Contains specialized structures called organelles.

Nucleus

• The nucleus controls cell activities.

• It is essential for cell division.

• Cells without a nucleus, like red blood cells, cannot divide.

• Individual parts of the nucleus are visible only under an electron microscope.

Nucleus Components:

• Chromosomes:

  • Long, thread-like structures within the nucleus.

  • Made of deoxyribonucleic acid (DNA) that carries hereditary information.

  • Condense into thick, rod-shaped structures during cell division.

• Nuclear Membrane:

  • Separates the contents of the nucleus from the cytoplasm.

Organelles in the Cytoplasm

• Endoplasmic Reticulum (ER):

  • Rough ER (RER)

  • Smooth ER (SER)

• Ribosomes

• Golgi Body

• Mitochondria

• Chloroplasts

• Vacuole:

  • Large and central in plant cells

  • Small and numerous in animal cells

Endoplasmic Reticulum (ER)

• Two types: rough ER (RER) and smooth ER (SER)

Ribosomes

• Small, round structures.

• Attached to RER or free in the cytoplasm.

• Responsible for protein synthesis.

Golgi Body

• Consists of flattened spaces surrounded by membranes.

• Functions:

  • Chemically modifies substances made by the ER.

  • Stores and packages substances in vesicles for secretion out of the cell.

Mitochondria

• Oval or sausage-shaped organelles.

• Site of aerobic respiration.

• Oxidizes food to release energy for cellular activities.

Chloroplasts

• Oval structures found in plant cells.

• Contain chlorophyll, a green pigment required for photosynthesis.

Vacuole

• Fluid-filled space enclosed by a partially permeable membrane.

• Stores substances within the cell.

• Plant Cell: typically has one large central vacuole containing sugars, mineral salts, and amino acids.

• Animal Cell: has numerous small vacuoles that store water and food temporarily.

Differences Between Plant and Animal Cells

How Are Cells Adapted to Their Functions?

Learning Outcome

• Explain how the structures of specialized cells are adapted to their functions (e.g., muscle cell, root hair cell, red blood cell).

Differentiation

• Cells in the human body perform specific functions.

• Examples: red blood cells, root hair cells, intestinal cells, and nerve cells.

• Differentiation is the process by which a cell becomes specialized for a specific function.

Red Blood Cell

Muscle Cell

Root Hair Cell

Stem Cells

• Stem cells can develop into other specialized cells.

• Scientists can grow cells of different organs in the laboratory and transplant them into humans.

• This has the potential to treat diseases that were once considered untreatable.