A2.2

Cell theory

All living organisms are made of one or more cells, cells are the basic structural unit of life, and new cells arise from pre-existing cells.

Deductive reasoning in cell theory

Using a general theory to predict specific outcomes, such as predicting a newly discovered organism will be made of cells.

Microscopy purpose

Microscopes allow observation of cells and structures too small to be seen with the naked eye.

Magnification

How many times larger an image is compared to the actual specimen.

Resolution

The ability to distinguish two objects that are close together as separate.

Light microscope resolution

Approximately 200 nm due to the wavelength of visible light.

Electron microscope resolution

Approximately 0.2 nm due to the short wavelength of electrons.

Electron microscopy advantage

Higher resolution and magnification allowing observation of organelles and viruses.

Freeze fracture microscopy

A technique that splits membranes to reveal internal membrane structure.

Cryogenic electron microscopy

Flash-freezing biological samples to preserve structure for high-resolution imaging.

Fluorescent staining

Use of dyes that emit light under UV to identify specific cell components.

Immunofluorescence

Use of fluorescent antibodies to bind and locate specific molecules.

Structures common to all cells

DNA, cytoplasm, and a plasma membrane.

Function of DNA

Stores genetic information and controls protein synthesis.

Cytoplasm composition

Mainly water with dissolved substances where metabolic reactions occur.

Plasma membrane structure

A phospholipid bilayer with embedded proteins.

Plasma membrane function

Controls movement of substances into and out of the cell.

Prokaryotic cell definition

A cell without a nucleus or membrane-bound organelles.

Prokaryotic cell size

Typically 0.1-5.0 µm.

Prokaryotic ribosomes

70S ribosomes used for protein synthesis.

Prokaryotic DNA

Naked circular DNA located in the nucleoid region.

Plasmids

Small circular DNA molecules that can carry additional genes.

Prokaryotic cell wall

Contains peptidoglycan and provides structural support.

Gram-positive bacteria

Bacteria with thick peptidoglycan walls that retain crystal violet stain.

Examples of Gram-positive bacteria

Bacillus and Staphylococcus.

Eukaryotic cell definition

A cell with a nucleus and membrane-bound organelles.

Eukaryotic ribosomes

80S ribosomes located in the cytoplasm or rough ER.

Nucleus function

Contains chromatin and controls cell activities.

Nuclear envelope

A double membrane with pores allowing transport of molecules.

Rough endoplasmic reticulum

Processes proteins synthesized by ribosomes.

Smooth endoplasmic reticulum

Synthesizes lipids and detoxifies substances.

Golgi apparatus

Modifies and packages proteins and lipids into vesicles.

Mitochondria

Site of aerobic respiration and ATP production.

Cristae

Folds of the inner mitochondrial membrane increasing surface area.

Lysosomes

Vesicles containing digestive enzymes for breakdown of materials.

Vesicles

Membrane-bound sacs for transport and storage.

Cytoskeleton

Network of microtubules and microfilaments providing structure and movement.

Microtubules

Tubulin-based structures involved in cell shape and transport.

Plant cell chloroplasts

Organelles responsible for photosynthesis.

Thylakoids

Membrane structures in chloroplasts containing chlorophyll.

Grana

Stacks of thylakoids within chloroplasts.

Stroma

Fluid matrix of the chloroplast where the Calvin cycle occurs.

Plant cell vacuole

Large permanent structure maintaining turgor and storage.

Tonoplast

Selective membrane surrounding the plant vacuole.

Plant cell wall

Cellulose-based structure providing rigidity.

Plasmodesmata

Channels connecting cytoplasm of adjacent plant cells.

Animal vs plant cells

Plant cells have cell walls, chloroplasts and large vacuoles; animal cells do not.

Fungal cell walls

Made of chitin and glucans.

Centrioles

Present in animal cells, absent in plants and fungi.

Cilia and flagella in animals

Used for movement or moving substances across surfaces.

Functions of life

Metabolism, reproduction, homeostasis, growth, response, excretion and nutrition.

Unicellular organism functions

All life functions carried out within a single cell.

Atypical cell structures

Cells with unusual structures adapted for specific functions.

Skeletal muscle fibres

Multinucleated cells formed by fusion.

Aseptate fungal hyphae

Multinucleated cells without septa.

Red blood cells

Lack nuclei to maximize space for haemoglobin.

Phloem sieve tube elements

Lack many organelles and rely on companion cells.

Identifying cells in micrographs

Based on presence of nucleus, cell wall, vacuole and organelles.

Biological drawing rules

Draw only what is seen, no shading, clear labels, include functions.

Endosymbiosis

One organism living inside another in a mutually beneficial relationship.

Endosymbiotic theory

Explains the origin of mitochondria and chloroplasts from prokaryotic cells.

Origin of eukaryotes

Evolved from a common unicellular ancestor with a nucleus.

Mitochondrial evidence for endosymbiosis

Circular DNA, 70S ribosomes, binary fission, double membrane.

Chloroplast evidence for endosymbiosis

Circular DNA, 70S ribosomes, replication and double membranes.

Cell differentiation

Process by which cells become specialized through gene expression.

Genome in multicellular organisms

All cells contain the same genes.

Gene expression in differentiation

Specific genes are switched on or off depending on function.

Environmental triggers of differentiation

Changes in environment influence gene expression.

Irreversibility of differentiation

Once specialized, most cells cannot change function.

Multicellularity

Evolution of organisms composed of many specialized cells.

Advantages of multicellularity

Larger size, cell specialization, and increased efficiency.

Tissues

Groups of similar cells performing a specific function.

Organs

Structures composed of multiple tissues working together.

Organ systems

Groups of organs working together to perform life functions.

Evolution of multicellularity

Occurred multiple times independently in evolutionary history.

Examples of multicellular organisms

Plants, animals, fungi and some algae.