IGCSE Biology

• The cell membrane is a selectively permeable barrier that separates the cell from its external environment.
• The cell uses a large portion of the chemical energy stored in the form of ATP for various cellular activities.
• Cellular respiration takes place in the mitochondria.
• The process of photosynthesis involves the conversion of light energy into chemical energy, which is stored as glucose.
• The nucleus is the control center of the cell, containing the genetic material (DNA) and responsible for regulating cell activities.
• Genes are segments of DNA that contain instructions for making specific proteins or RNA molecules.
• Protein synthesis occurs in two stages: transcription and translation.
• Plant cells have a rigid cell wall made up of cellulose fibers, while animal cells do not.
• Chloroplasts are organelles found only in plant cells where photosynthesis occurs.
• Glycolysis is the first stage of aerobic respiration, where glucose is broken down into pyruvate with the production of two ATP molecules.
• Chromosomes are thread-like structures made up of DNA molecules coiled around proteins called histones.
• ATP is used to power active transport, which moves substances against their concentration gradient.
• Cholesterol molecules can be embedded within the lipid bilayer to increase stability.
• mRNA serves as a template for ribosomes to synthesize proteins
• tRNA transports specific amino acids to the ribosome
• ribosomes makes protein in our body
• codons- code for single amino acid that will be joined together to make a protein
• anticodon- allows the tRNA to recognize and bind to the correct codon on the mRNA
• transcription- the process of making RNA from DNA. It occurs in the nucleus, makes mRNA which is the copied instructions with codons
• translation- the decoding of a mRNA message into a protein, happens in the ribosome and makes tRNA. the ribosomes makes a bond then kick out the anticodon
• dominant- a dominant allele only needs to be inherited by one parent in order for the characteristic to show up in the phenotype
• recessive- a recessive allele must be inherited from both parents in order for the characteristic to show up in the phenotype
• homozygous- an individual who has identical alleles for a particular gene
• heterozygous- having two different alleles for a particular gene
• phenotype- observable characteristics of an organism seen just by looking
• genotype- an organisms genetic composition
• codominance- two alleles are expressed equally, and neither allele is dominant or recessive
• genes- DNA segments that serve as the key functional units in hereditary transmission
• proteins- chains of amino acids that are made up of carbon, hydrogen, oxygen, and nitrogen
• mutations- caused by radiation, UV radiation and chemicals in our environment. mutations lead to cancer
• amino acids are the building blocks of proteins. 3 bases code for an amino acid
• the cornea is a transparent lens that refracts light as it enters the eye
• the iris controls how much light enters the pupil and controls the size of the pupil
• the lens is a transparent disc that can change shape to focus light onto the retina
• the retina contains light receptor cells the rods- detect light intensity and the cones- detect colour
• the optic nerve is the sensory neurone that carries impulses between the eye and the brain
• the pupil is the hole that allows light to enter the eye and is controlled by the iris
• in dark light the radical muscles contract. the ciliary muscles relax. the pupil is wide therefore more light is entering the eye
• in bright light the radical muscles are relaxed. the ciliary muscles contract and the suspensory ligaments are pulled tight. the pupil is narrow so less light enters the eye
• when an object is far away light is refracted less. the ciliary muscles are relaxed. the suspensory ligaments are pulled tight and the lens is thinner