Summary: Cell Structure

Table of Contents
1. Plant Cell
2. Cell Wall
3. Cell Membrane
4. Nucleus
5. Plastids
6. Other Organelles
7. Plant Cell Types
8. Plant Cell Functions
9. Animal Cell
10. Animal Cell Structure
11. Animal Cell Types
12. Differences Between Plant Cell and Animal Cell
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Plant Cell

• A eukaryotic cell with a true nucleus and membrane-bound organelles; distinguished from animal cells by an outer cell wall.
• Shape: generally rectangular and larger than many animal cells.

Cell Wall

• Outermost, usually non-living boundary; discovered by Robert Hooke.
• Middle lamella contains calcium and magnesium pectates and acts as a cement between cells.
• Cellulose is the main constituent; other components include hemicellulose, pectin, lignin, cutin and suberin.
• Structure: cellulose microfibrils form micelles → microfibrils → macrofibrils; other substances form the wall matrix.
• Synthesized by dictyosomes (Golgi) and sphaerosomes (lipid materials).
• Formation methods: Intussusception (deposition as fine grains) and Apposition (layer deposition); growth occurs by intussusception.
• Expansin loosens cellulose microfibrils to allow wall growth.
• Specialisations: lignification; pits (simple and bordered; bordered pits may have a torus); suberisation, cutinisation, cuticularisation, mucilage deposition, and silica deposition.

Cell Membrane

• Thin, semi-permeable layer of proteins and fats inside the cell wall; controls entry and exit of substances.

Nucleus

• Membrane-bound organelle storing DNA for division, metabolism and growth.
• Nucleolus: manufactures ribosomes.
• Nucleopore: pores in the nuclear membrane for movement of proteins and nucleic acids.

Plastids

• Membrane-bound organelles with their own DNA; involved in storage and synthesis.
• Leucoplasts: in non-photosynthetic tissues; store starch, proteins, lipids.
• Chloroplasts: contain chlorophyll; site of photosynthesis; stroma contains circular DNA.
• Chromoplasts: coloured plastids for pigment synthesis and storage (red, orange, yellow pigments).

Other Organelles

• Golgi apparatus: distributes synthesized macromolecules.
• Ribosomes: RNA-protein particles; sites of protein synthesis.
• Mitochondria: double-membraned; produce energy by breaking down carbohydrates.
• Lysosome: membrane-bound vesicles with digestive enzymes for waste disposal.

Plant Cell Types

• Collenchyma cells: provide flexible support when primary walls are not hardened.
• Sclerenchyma cells: more rigid due to hardening agents; provide strong support.
• Parenchyma cells: living cells for food production, gas exchange, storage and metabolism.
• Xylem cells: transport water and minerals from roots to other parts.
• Phloem cells: transport food made in leaves to the rest of the plant.

Plant Cell Functions

• Photosynthesis (in chloroplasts) - plants make food using sunlight, CO2 and water; energy produced as ATP.
• Transport of water, minerals and food by specialised cells (xylem and phloem).

Animal Cell

• A eukaryotic cell that lacks a cell wall but has a membrane-bound nucleus and other organelles.
• Sizes and shapes vary widely; most are microscopic and irregular in shape due to absence of a cell wall.

Animal Cell Structure

• Cell membrane: thin semipermeable layer of proteins and fats; protects the cell and controls transport.
• Nuclear membrane (nuclear envelope): double membrane around the nucleus.
• Nucleus: contains nucleolus, chromatin and DNA.
• Centrosome: near the nucleus; site of microtubule production.
• Lysosomes: membrane-bound vesicles with digestive enzymes for digestion, excretion and renewal.
• Cytoplasm: jelly-like matrix containing organelles; nucleoplasm is inside the nucleus.
• Golgi apparatus: manufacturing, packing and transport of cell particles.
• Mitochondrion: double-membraned energy organelle.
• Ribosomes: sites of protein synthesis.
• Endoplasmic reticulum (ER): membranous network originating from the nucleus.
• Vacuole: membrane-bound compartment for shape maintenance and storage (usually small and numerous in animal cells).
• Nucleopore: openings in the nuclear membrane for movement of molecules.

Animal Cell Types

• Skin cells
• Muscle cells
• Blood cells
• Nerve cells
• Fat cells

Differences Between Plant Cell and Animal Cell

• Shape: plant cells are square/rectangular; animal cells are irregular or round.
• Cell wall: present in plant cells; absent in animal cells.
• Plasma/cell membrane: present in both.
• Nucleus position: in plant cells often at one side; in animal cells generally central.
• Lysosomes: rare in plant cells; common in animal cells.
• Centrosomes: absent in plant cells; present in animal cells.
• Plastids: present in plant cells; absent in animal cells.
• Vacuoles: usually one large central vacuole in plant cells; small and numerous in animal cells.
• Cilia: absent in plant cells; present in many animal cells.
• Mitochondria: fewer in number in plant cells; numerous in animal cells.
• Mode of nutrition: plant cells are primarily autotrophic; animal cells are heterotrophic.