Tips: Biology Form 4

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INTRODUCTION TO BIOLOGY
HYPOTHESIS
A hypothesis makes a clear statement about a possible explanation for an observed 
phenomenon, and it can be tested.
FIXED AND CONTROL VARIABLES
Fixed or other control variables refer to other possible factors which may influence the 
outcome of the experiment, and such are kept constant throughout the experiment.
CELL STRUCTURE AND CELL ORGANISATION
ENDOPLASMIC RETICULUM
·         The rough endoplasmic reticulum (RER) is studded with numerous ribosomes on the outer surface of the membrane, and it is involved in protein synthesis while smooth endoplasmic reticulum (SER) lacks ribosomes and is more tubular than RER.
·         It is involved in lipid synthesis and transport of lipids and steroids.
NEGATIVE FEEDBACK
Negative feedback means that whenever a stimulus causes a change in a system, a corrective mechanism which reverses the original change bringing the system back to normal is activated.
MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE
CHOLESTEROL
The cholesterol helps regulate fluidity of the membrane and decreases the permeability of the membrane to ions.
PLASMA MEMBRANE
The plasma membrane has a selectively permeable nature due to
a.    Phospholipid bilayer being a selective barrier to molecules and ions
b.    Specificity of transport proteins on the membrane
DIFFUSION
·         Diffusion is the net movement of molecules and ions from an area of high concentration to an area of low concentration. Diffusion is a passive process where no energy is involved and substances can only move down their concentration gradient.
FOOD PRESERVATION
·         In food preservation, food preservatives make the surrounding solution hypertonic, thus water leaves the cell sap while the food preservative enters the food.
CHEMICAL COMPOSITION OF CELL
INTRACELLULAR AND EXTRACELLULAR ENZYMES
Intracellular enzymes are produced and retained in the cell itself, and extracellular enzymes are secreted from the cell.
AMINO ACIDS
Essential amino acids cannot be synthesized in the body, only non-essential amino acids can be.
CELL DIVISION
MITOSIS
Mitosis is a nuclear division that produces two genetically identical daughter nuclei, each containing the same number of chromosomes (same genetic information) as the parent nucleus.
GENETIC VARIATION
Meiosis leads to genetic variation by :
a.    Independent assortment of chromosomes:occurring in metaphase and resulting in random assortment of maternal and paternal chromosomes between daughter nuclei.
b.    Crossing over of segments of chromatids at chiasmata during prophase I forms new combinations of alleles and chromosomes of gamete cells.
NUTRITION
DEFAECATION
• Defaecation is the elimination of faeces which contains toxins and waste products such as bile pigments.
DEFICIENCY IN PROTEINS
• Deficiency in proteins causes :
a.    Kwashiorkor, characterized by body swelling and stunted growth
b.    Marasmus, characterized by thin and wrinkled skin
RESPIRATION
INTERNAL RESPIRATION
• Internal respiration or cellular respiration is the process of oxidising organic molecules to produce energy which is stored in ATP molecules.
NICOTINE
• Nicotine in cigarette smoke constricts blood vessels thus increasing blood pressure and the heartbeat rate.
DYNAMIC ECOSYSTEM
ABIOTIC COMPONENTS
·         Abiotic components of an ecosystem such as pH, temperature, light intensity, humidity, topography and microclimate affects the population and distribution of organisms in an ecosystem.
PROTISTA
·         Protista are simple eukaryotic organisms which may be unicellular, autotrophic, heterotrophic, and are mostly aquatic or live in moist conditions.
ENDANGERED ECOSYSTEM
EUTROPHICATION
·         Eutrophication which means a sudden and dramatic increase in nutrients in the water due to human activity, which disturbs and eventually destroys the food chain.
THIN OZONE LAYER
·         A thinner ozone layer will lead to increased UV radiation reaching the Earth’s surface. This causes an increase in incidence of cataracts and skin cancers in humans as it increase mutation rates.
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