Biology paper 2

• A stem cell is an undifferentiated cell capable of giving rise to many more cells of the same type
• Stem cells can differentiate into certain other cells
• Stem cells can be found in embryos, adult animals, and meristems in plants
• Stem cells from human embryos can be cloned and differentiated into most types of human cells
• Stem cells from adult bone marrow can form various types of cells, including blood cells
• Meristem tissue in plants can differentiate into any type of plant cell throughout the plant's life
• Stem cell treatment may help conditions like diabetes and paralysis
• Therapeutic cloning produces embryos with the same genes as the patient for medical treatment
• Stem cells from meristems in plants can be used to produce clones of plants quickly and economically
• Rare species can be cloned using stem cells to protect from extinction
• Crop plants with special features can be cloned for farmers, such as disease resistance
• Substances move into and out of cells via diffusion across cell membranes
• Diffusion is the movement of particles from an area of higher concentration to lower concentration
• Substances like oxygen, carbon dioxide, and urea are transported by diffusion in and out of cells
• Factors affecting diffusion rate include concentration gradient, temperature, and membrane surface area
• A single-celled organism has a large surface area to volume ratio for efficient molecule transport
• Water moves across cell membranes through osmosis
• Osmosis is the diffusion of water from a dilute to a concentrated solution through a partially permeable membrane
• Factors like rate of water uptake, percentages, and mass changes in plant tissue are important in osmosis
• Active transport moves substances from dilute to concentrated solutions, requiring energy from respiration
• Active transport allows mineral ions to be absorbed into plant root hairs from dilute soil solutions
• Sugar molecules are absorbed through active transport from lower concentrations in the gut into the blood
• Understanding of substances transport by diffusion, osmosis, and active transport is essential
• Differentiation between diffusion, osmosis, and active transport is important
• Exchange surfaces in multicellular organisms are specialized for efficient molecule transport
• Exchange surface effectiveness is increased by having a large surface area, thin membrane, and efficient blood supply
• Ventilation is crucial for gaseous exchange in animals
• Cell specialization is linked to active transport
• Cancer is the result of changes in cells leading to uncontrolled growth and division
• Benign tumours are growths of abnormal cells contained in one area, usually within a membrane
• Malignant tumour cells invade neighbouring tissues and spread to different parts of the body in the blood, forming secondary tumours
• Scientists have identified lifestyle risk factors for various types of cancer
• Genetic risk factors exist for some cancers
• Plant tissues include:

  • Epidermal tissues
  • Palisade mesophyll
  • Spongy mesophyll
  • Xylem and phloem
  • Meristem tissue found at the growing tips of shoots and roots
• The leaf is a plant organ
• Epidermis, palisade and spongy mesophyll, xylem and phloem, and guard cells surrounding stomata are key components
• Root hair cells, xylem, and phloem are adapted to their functions
• Changing temperature, humidity, air movement, and light intensity affect the rate of transpiration
• Stomata and guard cells control gas exchange and water loss
• Xylem transports water and mineral ions from roots to stems and leaves