CELL STRUCTURE AND ORGANISATION
Cell
-basic unit of structure and function in living organisms.
-Consists of cytoplasm and a nucleus (together called the protoplasm).
-Cytoplasm-liquid part of the cell, consists of about 70%-80% of water.
-Remaining part-dissolved organic and inorganic substances.

Nucleus
-Most important cell organelle in both plant and animal cells
-Controls activities of the cell.
-Contains genetic material DNA (Deoxyribo Nucleic Acid) and RNA(Ribo Nucleic Acid).
-Chromosomes (in nucleus) made of DNA and proteins.
-Genes (responsible for hereditary) found in the chromosomes.

Mitochondrion (si) Mitochondria(pl)
-Found in both plant and animal cells.
-Rod-like structures.
-Powerhouse of a cell as food substances oxidised and energy released in the form of ATP (Adenosine
Triphosphate) molecules for doing vital activities.

Ribosomes
-Small microscopic structures found in cytoplasm of both plant and animal cells.
-Usually found in groups called polyribosomes.
-Sites of protein synthesis [amino acids are brought over surfaces of ribosomes > form chains (polypeptide chains) which form protein molecules]

Vacuole
-In mature plant cells and consists of highly concentrated liquid (cell sap)
-Separated from cytoplasm by membrane-tonoplast.
-Young plant cells (maristematic cells) do not have vacuoles (nucleus in centre, dense cytoplasm).
Maristematic cells-root and shoot apexes.
-Generally animal cells do not contain vacuoles but sometimes only small vacuoles.

Lysosomes (suicide bodies)
-Minute bodies in cytoplasm of animal and plant cells.
-Contain powerful, hydrolytic enzymes-enable digestion of unwanted substances in cell.

Plastids
-Colouring bodies found in cytoplasm of plant cells.
-3 types:-leucoplasts(in root and tubers), chromoplasts(in fruits and petals) and chloroplasts(in green
leaves and stem).
-Chloroplasts-disc/bun-shaped structures. Pigment chlorophyll (in the membrane) traps light energy
during photosynthesis and converts it to chemical energy in the form of glucose.


Comparison between plant and animal cells
Plant cells:-
i)definite, fixed polygonal shape due to rigid cellulose cell wall. Also have plasma membrane
ii)3 types of plastids; leucoplasts, chromoplast and chloroplasts
iii) Mature cells contain large vacuole containing concentrated cell sap
iv)don't have centrioles

Animal cells:-
i)don't have cell wall, only flaccid plasma/cell membrane(made up of lipids and proteins)
ii)don't have plastids
iii)don't contain any vacuoles (generally)
iv )have centrioles.

Functions of the cell/plasma membrane
-plant cells-beneath cell wall. animal cells-outermost layer
-made of lipids and proteins.
- semi-/partially-/selectively-permeable membrane; controls substances entering and exiting the cell
-performs:-osmosis, diffusion, active transport

Osmosis
-movement of water molecules, region of (low conc./ high H₂O potential) > region of (high conc. /low H₂O potential), through a semi-permeable membrane
(H₂O movement; from soil water > root hairs, tissue fluids to cells and xylem to mesophyll cells.)

Water potential:
-Tendency for water to move from one place to another
-dilute solution -more water molecules (per unit) high water potential

Hypotonic solution:-sol. w/ a lower osmotic conc. (higher water potential) than another solution
-plant cell: water enters cell by (ex)osmosis, through plasma membrane, not cell wall > water enters vacuole > cell increases in size and pushes cell contents against cell wall, cell -> rigid or turgid

Plant cells don't burst: strong, inelastic cell wall.
turgor = rigidity of the cell w/ water
turgor pressure = pressure exerted by water on cell wall.
Animal cells-will swell and may burst (cell breakage or haemolysis).

Hypertonic solution-sol. w/ higher osmotic conc. (lower water potential) than another solution
-plant cell: water moves out of cell by (end)osmosis > vacuole decreases in size and cytoplasm shrinks away from cell wall > flaccid, plasmolysed (can be restored by placing in water or hypotonic sol.)
Animal cell-shrink > dehydrated/crenated

Isotonic solution-2 sol. of equal conc., cells will not change shape or size

Importance of tugor
Turgor pressure maintains shape of soft tissues in plants (young stems + leaves). When transpiration high
water lost > cells lose turgidity > plant wilts Plasmolysed tissues > killed if plasmolysed for too long. Plant wilts > dies unless sufficient water added > dilute soil solution.

Diffusion
-Random movement of molecules; region of high conc. > region of low conc.
-Osmosis + diffusion = passive processes as:- movement , towards conc. gradient (high to low), -doesn't use energy

Active Transport [affected by factors that affect respiration(e.g. oxygen and temperature concentration)]
-movement of molecules against concentration gradient (low to high).
-energy utilized [ATP (Adenosine Triphosphate) molecules, released during respiration]
(absorbing digested substances by villi in small intestines, uptake of mineral ions from soil by root hair cells)

ORGANISATION
ATOM > MOLECULE > ORGANELLES > CELL > TISSUE > ORGAN > ORGAN SYSTEM > ORGANISM
Cell:-Basic and fundamental unit of living organisms.
Tissue:-group of cells of similar origin, structure and function.
(Plants:-epidermis, xylem, phloem, cortex. Animals:-epithelium, muscles, nerves, etc.)
Organ:-composition of different tissues to carry out a specific function (eye-vision, flower-reproduction)
Organ System:-Consists of different organs to carry out a specific function.
(Nervous system:-brain, spinal cord and nerves. Transport system(plants):-xylem, phloem, etc)
Organism:-Collection of a number of organs systems on order to lead a normal life.


SPECIALISATION OF CELLS, TISSUES AND ORGANS
Root hair cells:
-Projection of finger-like structures into the surroundings, provides greater surface area for absorption of
water and mineral salts.
-Large vacuole - contained more concentrated cell sap - facilitates osmosis.
-Minute, thin and narrow structures, able to pass through intercellular spaces of soil particles.

Red blood cells: (erythrocytes) (white-leucocytes)(platelets-thrombocytes)
-Elastic biconcave cells, minute, able to squeeze through the thinnest blood capillaries.
-Being curved inwards (biconcave) provides more surface area for carrying oxygen.
-Presence of haemoglobin-combines w/ oxygen and forms highly unstable oxy-haemoglobin, which is
transported to all parts of the body. Dissociates w/ oxygen and oxygen is delivered to the cells.

Muscle fibres: (muscle cells)
-Skeletal muscle fibres-elongated and cylindrical in shape.
-Contain proteins called actin and myosin fibrils.
-Muscle fibres, contract and shorten and bring about movement of the body.

Xylem vessels
-Narrow elongated, perforated at their end walls.
-Large cell cavity (lumen) devoid of storage substances.
-Dead cells and protoplasm are absent.
-Arranged one below the other.
(All the above features enable them for efficient conduction of water and mineral salts within the plant.)
-Cell wall made of hard substance-lignin (lignified wall). It gives mechanical support to the plant. Lignin
strengthens walls and prevents collapse of vessel.


Enzymes
Nutrition
Transport in Plants
Support, Movement and Locomotion
Transport system in man-circulatory system
Respiration
Excretion
Homeostasis
The Eye
Nervous System
Chemical Control of Plant Growth
The Use and Abuse of Drugs
Diversity of Organisms
Nutrient cycles and Ecology
Parasitism
The Human Impact on the Environment
Reproduction in plants
Sexual reproduction in animals
Genetics

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