1. Building Blocks of Life

In brief:Cells are the fundamental units of all living organisms. Some organisms consist of one cell (unicellular) while others are made of many cells (multicellular).

Cells are the building blocks of all organisms. They are extremely small and require a microscope to view. Unicellular organisms (e.g. bacteria) consist of one cell; multicellular organisms are made of many cells.

Eukaryotic vs Prokaryotic Cells

Eukaryotic cells contain a nucleus and organelles (animals, plants, fungi). Prokaryotic cells lack a nucleus - their DNA is in a circular chromosome called a nucleoid (bacteria, archaea).

Animal vs Plant Cells

Feature	Animal Cell	Plant Cell
Cell wall	No	Yes (cellulose)
Chloroplasts	No	Yes
Vacuole	Small/temporary	Large, permanent
Cell membrane	Yes	Yes
Nucleus	Yes	Yes

Electron Microscopes

Light microscopes magnify up to ~400×. Electron microscopes magnify up to 1,000,000×, revealing cell ultrastructure. Transmission EM (TEM) shows internal structure; Scanning EM (SEM) shows surface detail.

Animal cell
Wikimedia Commons (public domain / CC)

Plant cell
Wikimedia Commons (public domain / CC)

Key Points

1Cells are the organisational unit of life
2Eukaryotic cells have a nucleus and organelles; prokaryotic cells do not
3Plant cells have a cell wall, chloroplasts, and large vacuole - animal cells do not
4Electron microscopes reveal ultrastructure not visible with light microscopes
5Protoplasm = nucleus + cytoplasm; cytoplasm = cytosol + organelles

Learning Outcomes

Describe the complexity of multicellular organisms
Compare the structure of prokaryotic and eukaryotic cells

2. Organelle Ultrastructure

In brief:Each organelle has a specific structure adapted to its function within the cell.

Cell Membrane

Made of a phospholipid bilayer with embedded proteins. It is selectively permeable, controlling what enters and exits the cell. Marker antigens on the surface identify the cell to the immune system.

Nucleus

Contains the cell's genetic material (DNA) in the form of chromatin (which coils into chromosomes during division). Surrounded by a double membrane with nuclear pores that allow mRNA to exit.

Mitochondria

The 'powerhouse' of the cell - site of aerobic respiration. Has a double membrane; inner membrane is folded into cristae (increases surface area for ATP production). Contains its own DNA and ribosomes.

Ribosomes

Tiny organelles where protein synthesis occurs. Found free in the cytosol or attached to rough endoplasmic reticulum.

Chloroplasts (Plant cells only)

Site of photosynthesis. Contains the green pigment chlorophyll in thylakoid membranes arranged in stacks called grana. The liquid between grana is the stroma.

Vacuole (Plant cells)

Large, permanent, fluid-filled sac. Maintains turgor pressure to keep the plant upright. Stores water, sugars, and waste products.

Cell Wall (Plant cells)

Made of cellulose. Provides structural support and prevents the cell from bursting. Adjacent cell walls are joined by the middle lamella.

Key Points

1Cell membrane is a selectively permeable phospholipid bilayer
2Nucleus contains DNA as chromatin/chromosomes, surrounded by nuclear envelope with pores
3Mitochondria have cristae for maximum ATP production
4Ribosomes are the site of protein synthesis
5Chloroplasts contain chlorophyll in thylakoid membranes (grana)
6Plant cell wall is made of cellulose; middle lamella joins adjacent walls

Learning Outcomes

Investigate, using primary data gathered with a light microscope and secondary data gathered from scanning electron microscope imagery, the structures and organelles of animal and plant cells and relate them to their functions

3. Cell Organisation & Stem Cells

In brief:Multicellular organisms are organised into cells, tissues, organs, and organ systems. Stem cells are undifferentiated cells that can become specialised.

Levels of Organisation

Cell → Tissue → Organ → Organ System → Organism

Tissue: A group of similar cells working together (e.g. muscle tissue, nervous tissue)
Organ: A structure made of different tissues working together (e.g. heart, leaf)
Organ system: A group of organs working together (e.g. digestive system)

Specialised Cells

Cells become specialised (differentiated) for specific functions. Examples: red blood cells carry oxygen; nerve cells transmit impulses; root hair cells absorb water.

Stem Cells

Stem cells are undifferentiated cells capable of dividing and developing into different cell types. They replace cells that die. Types include embryonic stem cells (can become any cell type) and adult stem cells (more limited).

Key Points

1Multicellular organisms are organised: cell → tissue → organ → organ system
2Specialised cells are adapted to specific functions
3Stem cells are undifferentiated and can develop into different cell types
4Stem cells replace dead or damaged cells in the body

Learning Outcomes

Describe the complexity of multicellular organisms