Key concepts in biology

• There are two types of cells: Eukaryotic (animals and plants) and prokaryotic.
• A eukaryotic cell contains a nucleus and membrane-bound organelles, while a prokaryotic cell does not.
• The components of both plant and animal cells include the nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes.
• Enzymes are biological catalysts that increase the rate of a chemical reaction without being permanently altered themselves.
• Genetic information is stored within the nucleus of a eukaryotic cell, arranged in chromosomes.
• The advantage of enzymes in the body is that they enable cellular reactions to take place at lower temperatures.
• The function of the nucleus is to control cellular activities.
• The active site of an enzyme is the region of an enzyme to which a substrate molecule binds and the reaction takes place.
• The cytoplasm is a fluid component of the cell that contains organelles, enzymes, and dissolved ions and nutrients.
• A haploid cell is a cell that contains a single copy of each chromosome (half the number of chromosomes), for example, 23 chromosomes in humans.
• Genetic information is stored in a prokaryotic cell as Chromosomal DNA which is a single large loop of circular DNA, Plasmid DNA which are small, circular loops of DNA found free in the cytoplasm and separate from the main DNA, and Ribosomes which are small structures found in the cytoplasm.
• A diploid cell is a cell that contains two copies of each chromosome (full set of chromosomes), for example, 46 chromosomes in humans.
• Plasmids carry genes that provide genetic advantages such as antibiotic resistance.
• Gametes are reproductive cells.
• The prokaryotic cell wall is composed of Peptidoglycan.
• A flagellum is a long, rotating, ‘whip-like’ protrusion that enables bacteria to move.
• The organelles found in prokaryotic cells include Chromosomal DNA, Plasmid DNA, Cell wall, Cell membrane, Ribosomes, and Flagella.
• The function of the cytoplasm is to serve as the site of cellular reactions.
• Ciliated epithelial cells are found lining the surface of structures such as the respiratory tract and uterus.
• Egg and sperm cells are haploid cells.
• Sperm cells contain a haploid nucleus that contains genetic information, a tail that enables movement, mitochondria that provide energy for tail movement, and an acrosome that contains enzymes that digest the egg cell membrane.
• Egg cells contain a haploid nucleus that contains genetic material, mitochondria in the cytoplasm that produce energy for the developing embryo, and cytoplasm that contains nutrients for the developing embryo.
• The function of ciliated epithelial cells lining the airways is to move in synchronised waves to beat mucus (containing dirt and pathogens) up to the back of the throat where it can be swallowed.
• Two haploid gametes fuse during sexual reproduction, resulting in an embryo with two chromosomes for each gene and two copies of each allele, making it diploid.
• The cell membrane of an egg cell hardens after fertilisation, preventing the entry of other sperm and ensuring the zygote is diploid.
• Enzymes are described as having a 'high specificity' for their substrate because only substrates with a specific, complementary shape can fit into an enzyme's active site.
• Total magnification of an image can be calculated from lens powers.
• A light microscope passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed.
• The electrons hit a fluorescent screen which emits visible light, producing an image.
• Magnification is the number of times bigger an image appears compared to the size of the specimen.
• Resolution is the smallest distance between two objects that can be distinguished.
• The disadvantage of light microscopes is their limited resolution.
• The magnification of an image can be calculated.
• The advantages of light microscopes include being inexpensive, easy to use, portable, and allowing the observation of both dead and living specimens.
• An electron microscope uses a beam of electrons which are focused using magnets.
• Large organic molecules must be broken down into smaller, simpler molecules in the body because they are too big to be absorbed across the surface of the gut wall.
• The units for rate are s-1.
• Enzymes have an optimum pH.
• Large molecules are broken down into smaller molecules for absorption into the bloodstream.
• The rate of a reaction can be calculated when given a value for time.