Summary Edexcel iGCSE Grade 9 Biology Notes ALL TOPICS

BIOLOGY END OF YEAR

TOPIC 1: NATURE AND VARIETY OF ORGANISMS

 MRS H GREN
o Movement- able to change position
o Reproduction- can produce offspring sexually or asexually
o Sensitivity- can adapt and respond to environment and stimuli
o Homeostasis- can maintain and control their internal environment
o Growth- can increase in mass and develop
o Respiration- can produce energy aerobically or anaerobically
o Excretion- can remove toxic waste products from body
o Nutrition- can absorb nutrients and use them for development such as growth
 Variety of organisms
 Eukaryotes (cells)
o Organisms that have a nucleus and organelles
 Organelles
 Nucleus- contains genetic material
 Cytoplasm- jelly-like substance where reactions occur
o Contains enzymes
 Cell membrane- controls what enters and leaves the cell
 Mitochondria- where aerobic respiration occurs producing energy
 Ribosomes- where protein synthesis occurs
o Plant cells
 Multicellular
 Contains chloroplasts where photosynthesis
occurs
 Cell walls are made of cellulose, making the cell
firm and protecting it
 Vacuole stores cell sap and keeps rigidity
 Carbs stored as starch
o Animal cells by Unknown Author is licensed
 E.g. mammals under
 Multicellular
 No chloroplasts, don’t photosynthesise
 No cell walls
 Carbs stored as glycogen
o Fungi
 Cell walls made of chitin
 E.g. yeast
 Stores carbs as glycogen
 Food from saprophytic digestion, where digestive
enzymes break down food so it can be absorbed
 Contains mycelium: a network of hyphae in a thread
like structure

, o Protoctists
 Single celled organisms
 Some have features which
resemble animal cells for example
amoeba
 Others resemble plant cells and
have chloroplasts, such as euglena


 Prokaryotes
o No nucleus or organelles bound by a membrane
o Bacteria
 E.g lactobacillus, used to make yoghurt
 Single celled, small
 Have a cell wall made of peptigoglycan
 No nucleus but have circular chromosomes of DNA
 Mainly eat off of other organisms but can do
photosynthesis
 Have cytoplasm and plasmids
o Virus
 Not a living organism
 Need a host to live
 Parasitic
 No cellular structure except DNA or RNA and a
protein coat


o Protists
 E.g. malaria
 Parasitic- use animals as hosts
 SPECIALISED CELLS
o Red blood cell
 Bi-concave shape maximises SA
 Haemoglobin carries oxygen
 Thin shape is mobile and flexible
 Nucleus breaks down to capacitate more oxygen
o Ciliated cell
 Lots of cilia (200) which clear passages
 Lots of mitochondria for maximum energy
 Cilia stops infections in the airways and lungs
o Nerve Cell
 Long axon to transmit messages
 Different sizes optimises message transmission
 Myelin sheath allows electrical impulses to travel quickly

o Sperm Cell
 Streamline

,  Large nucleus
 Mitochondria releases energy for movement
 Long tail to navigate through reproductive system
 Acrosomes store digestive enzymes to break down the outer layer of the
egg
o Palisade leaf cell
 Tightly packed, no gaps
 Lots of chloroplasts to optimise photosynthesis
o Root hair cell
 Large surface area for maximum water absorption
 Vascular bundle carries water, glucose and minerals
 Large vacuole speeds up movement of water

TOPIC 2: MOVEMENT ACROSS MEMBRANES
 Diffusion
o Random movement of particles from an area of higher concentration
to an area of lower concentration
o Factors affecting rate of diffusion
 Concentration gradient (steeper = faster)
 Surface area : volume ratio (larger SA = faster)
 Distance (shorter = faster)
 Temperature (higher = faster)
o Substances that enter cells
 Glucose
 Water
 Oxygen
 Amino acids
 Minerals
o Substances that are removed from cells
 Urea
 Carbon dioxide
 Osmosis
o Net movement of water from an area of higher WP to an area of
lower WP down a WP gradient
 WP: water potential, concentration of water molecules
 Through a partially permeable membrane
o Hypertonic solution: cell has a higher WP than solution
 Net movement out of cell
 Causes cells to shrivel
o Hypotonic solution: cell has a lower WP than solution
 Net movement into cell
 Can cause cell to explode or swell