IGCSE Biology 0610 - 2.1 Cell Structure

Objective: Describe the functions of cell structures in plant, animal and bacterial cells.

1. Animal Cells

Animal cells are eukaryotic cells, meaning they have a nucleus enclosed within a membrane. They are the fundamental building blocks of animals.

Here's a breakdown of key structures and their functions:

• Cell Membrane: A flexible outer boundary that controls what enters and exits the cell. It maintains the cell's internal environment.
• Cytoplasm: The jelly-like substance within the cell where organelles are located. It's the site of many chemical reactions.
• Nucleus: Contains the cell's genetic material (DNA) and controls the cell's activities.
• Mitochondria: The "powerhouses" of the cell. They carry out aerobic respiration, producing energy (ATP).
• Ribosomes: Responsible for protein synthesis. They can be found free in the cytoplasm or attached to the endoplasmic reticulum.
• Endoplasmic Reticulum (ER): A network of membranes involved in protein and lipid synthesis.
  • Rough ER: Has ribosomes attached and is involved in protein synthesis and modification.
  • Smooth ER: Lacks ribosomes and is involved in lipid synthesis and detoxification.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for transport within or outside the cell.
• Lysosomes: Contain enzymes that break down waste materials and cellular debris.
• Vacuoles: Store water, nutrients, and waste products. They are more prominent in plant cells.

2. Plant Cells

Plant cells are also eukaryotic but have some unique structures not found in animal cells, which contribute to the plant's structure and function.

Key structures and their functions:

• Cell Membrane: Same function as in animal cells – controls entry and exit.
• Cytoplasm: Same function as in animal cells – site of chemical reactions.
• Nucleus: Same function as in animal cells – controls cell activities.
• Mitochondria: Same function as in animal cells – aerobic respiration.
• Ribosomes: Same function as in animal cells – protein synthesis.
• Endoplasmic Reticulum (ER): Same function as in animal cells – protein and lipid synthesis.
• Golgi Apparatus: Same function as in animal cells – modification, sorting, and packaging.
• Vacuole: A large central vacuole that stores water, nutrients, and waste. It also helps maintain cell turgor pressure (rigidity).
• Cell Wall: A rigid outer layer made of cellulose that provides support and protection to the cell.
• Chloroplasts: Contain chlorophyll and are the site of photosynthesis, where light energy is converted into chemical energy (glucose).

3. Bacterial Cells

Bacteria are prokaryotic cells, meaning they lack a nucleus and other membrane-bound organelles. Their structure is simpler than eukaryotic cells.

Key structures and their functions:

• Cell Wall: A rigid outer layer that provides shape and protection. (Gram-positive and Gram-negative bacteria have different cell wall structures).
• Cell Membrane: Controls the passage of substances into and out of the cell.
• Cytoplasm: Contains the genetic material (DNA) in the form of a nucleoid.
• Ribosomes: Responsible for protein synthesis.
• Capsule: A sticky outer layer that provides protection and helps the bacteria adhere to surfaces.
• Flagella: Long, whip-like structures used for movement.
• Pili (Fimbriae): Short, hair-like structures used for attachment to surfaces.

Comparison Table

Structure	Animal Cell	Plant Cell	Bacterial Cell
Cell Membrane	Present	Present	Present
Cytoplasm	Present	Present	Present
Nucleus	Present	Present	Absent (Nucleoid)
Mitochondria	Present	Present	Absent
Ribosomes	Present	Present	Present
Endoplasmic Reticulum	Present	Present	Absent
Golgi Apparatus	Present	Present	Absent
Vacuole	Small	Large Central Vacuole	Absent
Cell Wall	Absent	Present (Cellulose)	Present (Peptidoglycan)
Chloroplasts	Absent	Present	Absent