Biology

• Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus.
• Meiosis is a type of cell division that produces gametes with half the normal chromosome number, essential for sexual reproduction.
• The function of the small intestine is to absorb nutrients from food.
• cells differentiate to become specialised. sperm cells are specialised for reproduction, nerve cells are specialised for rapid signaling, muscle cells are specialised for contraction, root hair cells are specialised for absorption and phloem and xylem cells are specialised for transport.
• Prokaryotic cells replicate by binary fission. This results in two daughter cells that have the same genetic information as the parent cell but can have differing numbers of plasmids.
• Eukaryotic cells are complex cells that have a nucleus and membrane bound organelles. All plant and animal cells are eukaryotic.
• Animal cells have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes.
• plant cells have a cell wall, chloroplasts, and a permanent vacuole in addition to the components usually found in an animal cell.
• Prokaryotic cells are smaller than eukaryotic cells and have a single circular strand of DNA instead of a nucleus. These cells also have a cell membrane, cell wall, cytoplasm and plasmids.
• Bacteria can be grown in a petri dish. They are grown in a nutrient broth (such as agar jelly). An inoculating loop can be used to transfer microorganisms to the dish.
• Stem cells are undifferentiated cells that can divide to produce more undifferentiated cells. These can be found in the bone marrow and in the embryo.
• Stem cells can be used to treat diseases such as diabetes, Parkinson's and spinal injuries. This is controversial as some people believe that each embryo is a potential human life.
• In plants stem cells are found in the meristems. These cells can be used to produce clones quickly and cheaply, grow more plants of a rare species, or produce plants with desirable characteristics.
• Diffusion: the spreading of particles from an area of high concentration to an area of low concentration.
• Dissolved substances can move in and out of the cell by diffusion. The cell membrane is semi-permeable The larger the surface area the faster the diffusion rate.
• Osmosis: the movement of water from a region of high water potential to a region of low water potential.
• Active transport is the movement of molecules from an area of low concentration to an area of high concentration against a concentration gradient. This requires energy from respiration. Active transport occurs in root hair cells in plants and in the gut in humans.
• Large, multicellular organisms have a low surface area : volume ratio. They need exchange surfaces for efficient diffusion. Exchange surfaces are found in the gills, lungs, skin and blood capillaries.
• Exchange surfaces are adapted to maximise efficiency of gas exchange. They have a large surface area, thin walls and a high blood flow.
• In humans, gas exchange happens in the lungs. Alveoli maximise diffusion by having a large surface area, thin walls, a moist lining and a large blood supply.
• The small intestine is covered in millions of small projections called villi. These increase the surface area of the small intestine so that food is absorbed more quickly into the blood.
• In plants, leaves are adapted to maximise potential for gas exchange. They spongy mesophyll and epidermis allow gas to diffuse through the leaf. Guard cells in the lower epidermis can open and close holes in the leaf, called stomata, to control the amount of gas entering or leaving the leaf.
• In fish, gills have a large surface area for gas exchange. Each gill is made of a large number of gill filaments. The gill filaments are covered in tiny structures called lamellae. Blood flows through the lamellae in one direction and water flows in the opposite direction, keeping the concentration gradient high.