cell diversity & differentiation

• Flower: Sexual reproduction
• Stem cell: an unspecialised cell that can express all its genes and undergo mitosis
• Animal Tissues
• Cells are very close to each other, forming continuous sheets
• Adjacent cells are bound together by lateral contacts (e.g tight junctions and desmosomes)
• No blood vessels
• Cells receive nutrients by diffusion from tissue fluid from underlying connective tissue
• Some have smooth surfaces, but others have either microvilli or cilia
• Have short cell cycles and divide up to 2-3 times a day to replace worn/damaged cells
• E.g blood, bone, cartilage, tendons, ligaments, skin
• Widely distributed in the body
• Consists of a non-living extracellular matrix containing proteins (collagen and elastin) and polysaccharides (e.g hyaluronic acid which traps water)
• Hold structures together
• Provides support
• Matrix separates the living cells in the tissue enabling it to withstand forces (e.g weight)
• Chondroblasts: immature cells in cartilage → secrete extracellular matrix
• Chondrocytes: mature, less active cells → maintain the matrix
• There are 3 types: Hyaline, Fibrous, Elastic.
• Well vascularised (has many blood vessels)
• Fibres: muscle cells → they are elongated
• Contain myofilaments (special organelles made of proteins actin and myosin) which allow the tissue to contract
• Allow movement
• There are 3 types: Skeletal, Cardiac, Smooth.
• Meristematic cells have thin walls, contain very little cellulose, no chloroplasts, do not have a large vacuole, and can divide by mitosis and differentiate into other types of cells.
• The brain, spinal cord, nerves are part of the nervous system which is responsible for communication, control, coordination, and endocrine functions.
• Osmoregulation is important in the integumentary system which includes skin, hair, nails.
• Tissue structure, function, and meristematic cells are important in understanding plant tissues.
• The skeleton and skeletal muscles provide support, protection, movement, and immunity in the musculo-skeletal system.
• Excretion occurs in kidneys, ureters, bladder.
• The lymph system includes lymph nodes, vessels which transport fluid back to the circulatory system and are important in resisting infections.
• Epidermal tissue consists of flattened cells that lack chloroplasts (other than guard cells) and form a protective covering over leaves, stems and roots.
• Vascular tissue consists of two types, both present in vascular bundles: Xylem which carries water and minerals from roots to rest of the plant, and Phloem which transfers products of photosynthesis (sucrose) from leaves to plant parts that don’t do this.
• Xylem is derived from meristems by depositing lignin in their cell walls to reinforce and waterproof them, ending of the cells break down to form continuous columns with wide lumens to carry water and dissolved minerals, and phloem is derived from meristems by losing most of their organelles, developing sieve plates between tubes, and retaining organelles in companion cells.
• Airways (trachea, bronchus, bronchioles), lungs, diaphragm, intercostal muscles are involved in breathing and gas exchange.
• Glands that make hormones such as thyroid, testes, ovaries, adrenal, pancreas are part of the endocrine system.
• The reproductive system includes testes, penis, ovaries, uterus, vagina.
• Leaf function is photosynthesis, root function is anchorage in soil, absorption of mineral ions and water, storage, stem function is support, holds up leaves to get more sunlight, transportation of water and mineral ions, transportation of photosynthesis products, and storage of photosynthesis products such as starch and sugars.
• Meristematic cells contain stem cells and are found at the root and shoot tips and in the cambium of vascular bundles.