Cells and organisation

Study Notes

Cells are the basic building blocks of all living things, providing structure and performing essential functions. Animal and plant cells have similarities and differences in their structures and organelles. Levels of organisation in biology include cells, tissues, organs, and organ systems.

• Cell — the basic functional and structural unit in a living organism.
  Example: Human body cells.
• Nucleus — serves as the cell’s command center, housing DNA.
  Example: Nucleus in animal and plant cells.
• Plasma membrane — the outer lining of the cell that controls entry and exit of materials.
  Example: Plasma membrane in both animal and plant cells.
• Cytoplasm — jelly-like fluid inside the cell that surrounds the nucleus.
  Example: Cytoplasm in animal and plant cells.
• Mitochondria — organelles that convert energy from food into usable cell energy.
  Example: Mitochondria in muscle cells.
• Cell wall — a rigid layer providing structural support, found only in plant cells.
  Example: Cell wall in plant cells.
• Chloroplast — organelle where photosynthesis occurs, containing chlorophyll.
  Example: Chloroplasts in leaf cells.
• Tissue — a group of similar cells working together to perform a function.
  Example: Muscle tissue.
• Organ — made from different tissues working together to perform specific functions.
  Example: Heart.
• Organ system — groups of organs with related functions working together.
  Example: Digestive system.

Exam Tips

Key Definitions to Remember

• Cell
• Nucleus
• Plasma membrane
• Cytoplasm
• Mitochondria
• Cell wall
• Chloroplast
• Tissue
• Organ
• Organ system

Common Confusions

• Confusing the function of the nucleus with the mitochondria.
• Mixing up the presence of cell walls in animal cells.
• Misunderstanding the difference between tissues and organs.

Typical Exam Questions

• What is the function of the nucleus?
  It serves as the cell’s command center and houses DNA.
• How do plant and animal cells differ in structure?
  Plant cells have a cell wall and chloroplasts; animal cells do not.
• What are tissues and how do they relate to organs?
  Tissues are groups of similar cells, and organs are made from different tissues.

What Examiners Usually Test

• Differences between plant and animal cells.
• Functions of various cell organelles.
• Understanding of levels of organisation from cells to organ systems.