Biology Key Points for O Level

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Cell structure and organization
• Chloroplasts
o Site of photosynthesis where light energy is absorbed
o Consist of grana which are stacked up to increase surface area for absorption of light
o Only present in plant cells
• Cell membrane (plasma membrane)
o Lipid bilayer that surrounds the cell, interspersed with protein molecule o Presence of temporary pores
o Selectively permeable
 Controls movement of substances
o Diffusion, osmosis and active transport can therefore take place o Prevent outflowing of cytoplasm
o Tonoplast
 Plasma membrane surrounding the vacuole
• Cell wall
o Made of cellulose (a polysaccharide), and may be deposited with ligin o Maintain cell turgidity, provide mechanical support, protect from mechanical damage
o Freely permeable to water and most solutes
o Only present in plant cells
• Cytoplasm
o Protoplasm surrounding the nucleus
o There are numerous organelles present in the cytoplasm
o Organelle
 Specialized membrane bound structures
• Cell vacuole
o Fluid-filled space enclosed by a membrane
o In animal cells, these are present as numerous small ones, and these are usually not permanent
o In plant cells, there is usually a large central vacuole
o Cell sap
 Fluid in vacuoles, contains sugars, mineral salts and amino acids
o Tonoplast
 Membrane around the vacuole
• Nucleus
o Nucleoplasm
 Small spherical mass of denser protoplasm
o Nuclear membrane
 Nuclear envelope
o Found in the cytoplasm
o Control activities of the cell
 Reproduction, repairs and maintenance
o Chromatin
 Network of long thread-like structures, containing the heredity materials
o Chromatin is made up of proteins and DNA (Deoxyribose Nucleic Acid) o Chromosomes

Condensed and highly coiled chromatin threads during cell
division
o Nucleoli
 A spherical structure that plays a part in the build up of proteins
• Endoplasmic reticulum
o A series of flattened sheets
o Smooth endoplasmic reticulum
 Sites of synthesis and transport of steroids and lipids
o Rough endoplasmic reticulum
 Transport proteins synthesized at the ribosomes towards Golgi bodies for secretary packing
• Mitochondria
o Rod-shaped
o Site of aerobic respiration
o Powerhouse
 Release energy during cellular respiration
• Golgi bodies
o Stacks of flattened membrane sacs
o Involved in secretion of vesicles, formation of lysosomes
• Ribosomes
o Tiny structures concerned with the manufacture of proteins o Found on rough endoplasmic reticulum
• Comparison between plant cell and animal cell
Plant cell
Animal cell
Cell wall

X
Cell membrane


Chloroplasts

X
Mitochondria


Golgi apparatus


Endoplasmic reticulum


Nucleus


Shape
Fixed
Irregular
Centriole
X

Vacuoles
One large central
Many small
Granules
Starch
Glycogen
Cilia/flagella
X

o All cells have cell membrane, cytoplasm, nucleus, mitochondria, endoplasmic reticulum and ribosomes
• Root hair cell
o Function
 Increase absorption of water and mineral salts from the soil o Presence of root hair
o Long and elongated
o Increase surface area for greater rate of absorption
• Xylem vessel
o Function
 Conduction of water in plants as well as to offer mechanical support
o Narrow and cylindrical continuous tube
o Absence of cross wall











o Water column can move easily up the lumen of the xylem vessel o Lignified cell walls
o Strengthens the wall and prevents collapse of the xylem vessel Red blood cell
o Function
 Transport of oxygen from lungs to the rest of the body
o Contains hemoglobin
 Oxygen carrier
o Flat, biconcave shape (no nucleus)
o This serves to increase surface area to volume ratio
o Oxygen can also diffuse into or out of the cell at a faster rate o The absence of a nucleus also allow the red blood cell to squeeze through the narrow capillaries
Cell
o Basic structural unit of all organisms
o Functional unit of all organisms where all chemical...
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