Cell Structure and Organisation

Organisation of the Organism

• Focuses on cell structure, specialised cells, levels of organisation, and size of specimens.

Cell Structure & Organisation

• Cytoplasm contains all other cell structures inside the cell.
• A nuclear membrane surrounds the large nucleus, separating it from the cytoplasm.
• The cell membrane surrounds the cell.
• Plant cells have a cell wall made of cellulose that surrounds the cell membrane.
• Chloroplasts are organelles in the cytoplasm that contain chlorophyll.
• Vacuoles are large vesicles that compose a large part of the plant cell interior.
• Mitochondria are organelles scattered throughout the cytoplasm.
• Ribosomes are structures either free in the cytoplasm or attached to endoplasmic reticulum.
• Rough Endoplasmic Reticulum (R.E.R.) contains ribosomes. Vesicles are structures moving throughout the cytoplasm.

Cell Structures and Functions

• Nucleus: Contains chromosomes to control how cells grow, work, and divide.
• Cytoplasm: Supports cell structures, facilitates chemical reactions, and contains water and solutes.
• Cell Membrane: Holds the cell together and controls substance movement.
• Cell Wall: Provides support and defines the cell's shape.
• Chloroplasts: Facilitate photosynthesis, using chlorophyll to absorb light energy.
• Vacuole: Contains cell sap, stores various materials, and supports cell shape.
• Mitochondria: Aerobic respiration occurs here, providing energy; more reactions mean more mitochondria.
• Ribosomes: Site for protein production.
• Vesicles: Transport substances between cell parts.

Specialised Cells

• Specialised cells have specific characteristics for particular functions, controlled by genes in the nucleus.
• Cells differentiate to gain necessary structures and characteristics for their roles.

Examples of Specialised Cells in Animals

• Ciliated cell: Cilia move mucus containing trapped particles out of the trachea and bronchi.
• Nerve cell: Long to reach different body parts, possessing extensions to communicate with other cells, insulated by a fatty sheath for faster impulse transmission.
• Red blood cell: Biconcave shape maximizes oxygen diffusion, contains hemoglobin to bind and transport oxygen, and lacks a nucleus to carry more hemoglobin.
• Sperm cell: Head contains a haploid nucleus for fertilization; acrosome has digestive enzymes; mid-piece packed with mitochondria for energy; tail enables swimming.
• Egg cell: Contains nutrient-rich cytoplasm for early embryo growth and a haploid nucleus for fertilization; membrane changes post-fertilization to prevent further sperm entry.

Examples of Specialised Cells in Plants

• Root hair cell: Absorbs water and mineral ions with an increased surface area due to root hairs, thin walls for quick water passage, and no chloroplasts.
• Xylem vessel: Conducts water and supports the plant, forms continuous columns as cells die, lack organelles. Lignin thickens cell walls.
• Palisade mesophyll cell: Column-shaped to absorb sunlight and packed with chloroplasts for maximum photosynthesis.

Levels of Organisation

• Cells: Basic units in organisms.
• Tissues: Similar cells performing the same function
• Organs: Different tissues working together with specific functions.
• Organ Systems: Organs with related functions working together.
• Shoot System: Leaf, stem, flower and fruit with tissues like epidermis, mesophyll, xylem and pholem
• Root System: Root and tuber with tissues xylem, pholem and ground tissue
• Digestive System: Esophagus, stomach, and intestines with tissues muscle, connective, nerve, and epithelial
• Circulatory System: Heart, veins, and arteries with tissues muscle, connective, nerve and epithelial
• Immune System: Thymus and spleen with bone marrow tissue
• Respiratory System: Trachea, bronchi and lungs with connective, muscle and epithelial tissue
• Excretory System: Liver, kidney, skin and lungs with muscle, connective, epithelial and nerve tissue
• Nervous System: Brain and spinal cord with nerve tissue
• Reproductive System: Ovary, cervix, uterus, vagina, testes and penis with muscle, connective, nervous and erectile tissue

Calculating Magnification & Specimen Size

• Magnification is calculated using the formula: Magnification = Image Size / Actual Size.
• To calculate another value becomes easier using the equation triangle.
• Magnification lacks units.
• 1 cm = 10 mm
• 1 mm = 1000 μm
• 1 cm = 10,000 μm