Cambridge Syllabus Notes

2.1 Cell Structure

Cells are the building blocks of life. Think of a cell as a tiny factory where every part has a job. 🏭 The main structures are like the factory’s departments: the cell membrane is the security gate, the nucleus is the manager, and the ribosomes are the workers that build proteins.

Key Cell Structures

Cell membrane – a phospholipid bilayer $C_{32}H_{64}O_{12}P_2$ that controls what enters and leaves the cell. It’s like a smart door with gates (channels) and locks (transport proteins).
Cytoplasm – the jelly‑like fluid that holds organelles. Imagine it as the factory floor where everything moves.
Nucleus – contains DNA and directs cell activities. Think of it as the office with a nuclear envelope that keeps the manager (DNA) safe.
Ribosomes – tiny machines that read RNA and assemble amino acids into proteins. They’re the assembly line workers.
Endoplasmic reticulum (ER) – rough ER has ribosomes (protein factories), smooth ER makes lipids. It’s the production line.
Golgi apparatus – packages proteins for transport. Think of it as the post office.
Vacuoles – storage sacs. In plant cells, the central vacuole is like a warehouse holding water, ions, and nutrients.
Mitochondria – powerhouses that produce ATP. They’re the power plant of the cell. $ATP = ADP + Pi$
Chloroplasts – only in plant cells, convert light into energy via photosynthesis. They’re the solar panels.
Cell wall – rigid outer layer in plant, fungal, and bacterial cells. It’s the building’s exterior wall that gives shape and protection.

For a spherical cell, the volume can be calculated using the formula:

$$V = \frac{4}{3}\pi r^3$$

Plant Cell

Structure	Function
Cell wall	Provides shape, support, and protection. Made of cellulose.
Chloroplasts	Photosynthesis – convert light into glucose. 🌞
Central vacuole	Stores water, ions, pigments; maintains turgor pressure.
Plasmodesmata	Channels that connect cells for communication and transport.
Other organelles	Nucleus, mitochondria, ER, Golgi, ribosomes – same as animal cells.

Photosynthesis in chloroplasts follows the equation:

$$6CO_2 + 6H_2O + light \rightarrow C_6H_{12}O_6 + 6O_2$$

Animal Cell

Structure	Function
Cell membrane	Selective barrier; controls transport.
Nucleus	DNA storage and control center.
Mitochondria	ATP production – the energy factory. $ATP = ADP + Pi$
Rough ER & Golgi	Protein synthesis and packaging.
Smooth ER	Lipid synthesis, detoxification.
Lysosomes	Break down waste and foreign material.
Centrosomes & Centrioles	Organise microtubules during cell division.

Bacterial Cell

Structure	Function
Cell wall (peptidoglycan)	Provides shape and protection; target of antibiotics.
Plasma membrane	Selective barrier; controls transport.
Cytoplasm	Contains ribosomes, DNA (plasmids), and enzymes.
Nucleoid	Region where circular DNA is located.
Ribosomes	Protein synthesis.
Flagella / Pili	Movement and attachment.
Capsule	Protects against host defenses.

Cell division in bacteria is a simple process:

$$Cell \rightarrow 2 \, Cell$$

Exam Tips & Quick Reference

When marking diagrams, label all visible structures – the more you identify, the higher your score.
Remember the unique features of each cell type: plant cell wall, chloroplasts, central vacuole; animal cell lacks these but has centrioles; bacterial cells have a nucleoid and peptidoglycan wall.
Use the “key” in the diagram to match structures to names.
Practice drawing a plant, animal, and bacterial cell from memory – this helps you recognise structures quickly.
For multiple‑choice questions, look for process clues (e.g., “photosynthesis” → chloroplast).

Identify the cell structures in diagrams and images of plant, animal and bacterial cells.