biology paper 1- mine

• Root Hair Cell


  Plants absorb water from the soil by osmosis. Root hair cells are adapted for this by having a large surface area to speed up osmosis. The absorbed water is transported through the roots to the rest of the plant.
• Xylem


  Xylem vessels are involved in the movement of water through a plant from its roots to its leaves (in one direction only). Water is absorbed from the soil through root hair cells, transported through the xylem vessels up the stem to the leaves, and evaporates from the leaves (transpiration). Xylem contains lignin.
• Xylem and Phloem


  • Transport in xylem is a physical process, it is a hollow tube with water flowing in one direction. Transport in phloem requires energy (comes from companion cell) and transports glucose and amino acids in both directions.
• How plants grow


  1. Zone of cell division

  2. Zone of cell elongation

  3. Zone of cell differentiation
• Elongate


  In the growing areas, plant cells become longer and grow before they differentiate.
• Redifferentiate


  Plant cells can become a different specialised cell even after they have first differentiated.
• How the leaf structure is adapted to maximise photosynthesis

  • Large Surface Area
  • Thin blades
  • Large air spaces between cells
  • Vascular tissue in the midrib and veins
• Stomata


  Plants have stomata to obtain carbon dioxide from the atmosphere and to remove oxygen and water vapour produced in photosynthesis. They are where gas exchange takes place in the plant, with the gases moving in and out via diffusion.
• Water loss during photosynthesis

  Stomata are found on the underside of leaves, each surrounded by two guard cells. During photosynthesis, low carbon dioxide levels cause guard cells to become turgid, curving out and opening the stoma. High carbon dioxide levels cause the guard cells to lose water, closing the stoma and preventing further water loss.
• If the stomata were permanently open, the plant would continue to lose water until it dried up.
• Leaf adaptations to prevent excess water loss

  • Waxy cuticle
  • Most stomata on underside of leaves
  • Guard cells close stomata when water is scarce
• Translocation


  Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. Phloem is composed of tubes of elongated cells with pores in the end walls, allowing cell sap to move from one phloem cell to the next.
• Factors affecting the rate of transpiration

  • Temperature
  • Humidity
  • Wind speed
  • Light intensity
• Measuring Transpiration Rates


  1. Independent: Time

  2. Dependent: Distance moved by air bubble

  3. Control: draughts, water source, temperature
• Adaptations of plants to reduce transpiration

  • Leaves reduced to spines
  • Reduced number of stomata
  • Waxy leaf cuticle
  • Rolled leaves, leaf hairs, and stomata sunk in pits
• TMV Tobacco Mosaic Virus


  Spreads through contact between diseased and healthy plants and insects that act as a vector. Symptoms include discoloured plant leaves that prevents photosynthesis and proper growth.
• Signs of plant disease

  • Unusual growths
  • Spots or discoloured leaves
  • Malformed leaves or stems
  • Presence of pests
  • Stunted growth
  • Areas of decay (rot)
• Effects of mineral ion deficiencies in plants

  • Nitrate ions = healthy growth
  • Lack of nitrate = stunted growth
  • Magnesium = healthy chlorophyll
  • Lack of magnesium = chlorosis (yellowing of leaves due to lack of chlorophyll)
• Photosynthesis


  1. Carbon dioxide + water -> glucose + oxygen (light)

  2. Carbon dioxide from the air, absorbed through the stomata

  3. Water from the soil, absorbed into the roots by osmosis, moved via xylem up the stem to the leaves

  4. Oxygen released through the stomata by diffusion

  5. Some glucose used for respiration, some converted to starch, cellulose, fats/oils, proteins
• Factors that may limit the rate of photosynthesis

  • CO2 concentration
  • H2O
  • Light intensity
  • Temperature
  • Chlorophyll
• GCSE Required Practical - Light and Photosynthesis

  1. To find out what happens to the rate of photosynthesis when we change the light intensity

  2. Potential sources of error: difficult to count very small bubbles, heat from the lamp

  3. Need to leave the plant to adjust before starting measurements

  4. Other limiting factors apart from light: temperature and CO2
• Auxin


  A plant hormone that causes shoots to grow upwards and roots to grow downwards (gravitropism), and stems to grow towards light (phototropism).
• Deforestation (cutting down forests/rainforests) increases CO2 in the atmosphere, reduces photosynthesis, and decreases biodiversity.