Biology paper 1 spec

• Cells are the basic unit of all forms of life
• Structural differences between types of cells enables them to perform specific functions within the organism
• Differences in cells are controlled by genes in the nucleus
• Stem cells

  Undifferentiated cells of an organism which are capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation
• Eukaryotic cells (plant and animal cells)

  • Have a cell membrane, cytoplasm and genetic material enclosed in a nucleus
• Prokaryotic cells (bacterial cells)

  • Are much smaller in comparison, have cytoplasm and a cell membrane surrounded by a cell wall, the genetic material is not enclosed in a nucleus but is a single DNA loop and may have small rings of DNA called plasmids
• Animal cells

  • Have a nucleus, cytoplasm, cell membrane, mitochondria, ribosomes
• Plant cells

  • In addition to the parts found in animal cells, often have chloroplasts and a permanent vacuole filled with cell sap, and a cell wall made of cellulose
• Cell differentiation


  As an organism develops, cells differentiate to form different types of cells. Most types of animal cell differentiate at an early stage, while many types of plant cells retain the ability to differentiate throughout life
• An electron microscope has much higher magnification and resolving power than a light microscope, enabling biologists to see and understand many more sub-cellular structures
• Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature
• Preparing an uncontaminated culture using aseptic technique


  Sterilise Petri dishes and culture media before use, sterilise inoculating loops by passing through a flame, secure lid of Petri dish with adhesive tape and store upside down, incubate cultures at 25°C
• The nucleus of a cell contains chromosomes made of DNA molecules, and in body cells the chromosomes are normally found in pairs
• Stages of the cell cycle, including mitosis


  DNA replicates to form two copies of each chromosome, one set of chromosomes is pulled to each end of the cell and the nucleus divides, cytoplasm and cell membranes divide to form two identical cells
• Cell division by mitosis is important in the growth and development of multicellular organisms
• Stem cells

  Can give rise to many more cells of the same type, and from which certain other cells can arise from differentiation
• Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells, and stem cells from adult bone marrow can form many types of cells including blood cells
• Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant
• Therapeutic cloning produces an embryo with the same genes as the patient, so stem cells from the embryo are not rejected by the patient's body
• The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections
• Stem cells from meristems in plants can be used to produce clones of plants quickly and economically, to protect rare species from extinction or produce large numbers of identical crop plants with special features
• Diffusion

  The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
• Factors affecting the rate of diffusion are the concentration gradient, temperature, and surface area of the membrane
• A single-celled organism has a relatively large surface area to volume ratio, allowing sufficient transport of molecules into and out of the cell
• In multicellular organisms, surfaces and organ systems are specialised for exchanging materials, to allow sufficient molecules to be transported into and out of cells for the organism's needs
• Osmosis

  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Active transport

  Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient), requiring energy from respiration
• Cells are the basic building blocks of all living organisms
• Tissue

  A group of cells with a similar structure and function
• Organ

  Aggregations of tissues performing specific functions
• Organ system

  Organs organised to work together to form organisms
• Many interventions would not be necessary if individuals reduced their risks through improved diet and lifestyle
• The plant's transport system is dependent on environmental conditions to ensure that leaf cells are provided with the water and carbon dioxide that they need for photosynthesis
• Cells

  Basic building blocks of all living organisms
• Tissue

  Group of cells with a similar structure and function
• Organ system

  Organs that work together to form organisms
• The digestive system is an example of an organ system in which several organs work together to digest and absorb food
• Enzymes

  Catalyse specific reactions in living organisms due to the shape of their active site
• Lock and key theory

  A simplified model to explain enzyme action
• Digestive enzymes

  • Carbohydrases (e.g. amylase)
  • Proteases
  • Lipases