bio WA1 '24

• During a disease outbreak, people are advised to wear a mask and exercise social distancing to prevent the spread of infectious diseases through droplets in the air
• Sexually Transmitted Infections (STIs) like HIV can be transmitted through direct contact, such as exchanging body fluids during sexual intercourse
• bacterial cell genetic material: small circular DNA molecules
• palisade mesophyll cell adaptations: contains lots of chloroplasts so more photosynthesis can be carried out per cell, and is situated right below upper epidermis to receive as much sunlight as possible for photosynthesis, tightly packed long and cylindrical cells so more photosynthetic cells can be present
• waxy cuticle function: waterproof to prevent water loss through evaporation from leaf, transparent to allow light to reach mesophyll cells for photosynthesis
• stomata located on lower surface of leaf: reduce water loss through transpiration
• thin film of moisture on mesophyll cells surface: allow CO2 to dissolve through and diffuse through the cells
• leaf blade: large and flat to increase surface area to volume ratio, enabling, max amt. of light to be absorbed for photosynthesis and CO2 to reach inner cells more quickly with shorter diffusion distance
• intercellular air spaces allow for diffusion of CO2 and O2
• stomata: allow CO2 and O2 to diffuse in and out of the leaf
• guard cells: manufacture glucose by photosynthesis
• guard cells: control opening of stomata
• chlorophyll absorbs energy from light during photosynthesis and transfers it to chemical stores in carbohydrates which are synthesised from water and carbon dioxide
• choroid: pigmented black to prevent internal reflection in the retina, contains blood vessels that bring oxygen and nutrients to eye
• xylem: made up of dead cells that have no chloroplast or cross-walls, reducing resistance to water flowing through
• xylem inner walls are strengthened by lignin which is deposited in the form of annular rings, spirals, or the whole vessel except regions called pits is lignified, providing mechanical support to the xylem
• long and narrow root hair increases surface area to volume ratio of root hair cell, increasing rate of absorption of water and mineral salts
• translocation studies 1 : 'ringing' experiment, phloem removed; stem above cut region swells up as food subst from leaves cannot reach stem below cut region.
• translocation studies 2: use of aphids, body of aphid is cut off, leaving feeding stylet in plant tissues, liquid exudes from cut end of stylet ann analysis of liquid shows sucrose and a.a present

  feeding stylet is inserted into phloem sieve tube, showing translocation of sugars and a.a occurs in phloem
• translocation studies 3: use of isotopes, leaf is provided with CO2 containing carbon-14 radioactive isotope (presence detected by x-ray photographic film). As photosynthesis takes place, sugars formed will contain radioactive carbon, stem is cut and exposed to x-ray photographic film, radioactive subst is present in phloem as the radioactive subst causes x-ray film to darken
• translocation: transport of manufactured food substances e.g sugars and a.a in plants
• transpiration: loss of water vapour from aerial parts of a plant, mainly through stomata of leaves
• photosynthesise: process CO2 and H2O is converted to glucose and O2, in presence of light and chlorophyll
• limiting factor: any factor directly affecting rate at which a chemical reaction occurs if its quantity is changed
• root hairs absorb ions in soil solution against concentration gradient by active transport as conc of ions in soil solution is lower than that of root hair cell sap
• energy for active transport in uptake of ions in root hair cell comes from cellular respiration in root hair cell
• increasing CO2 conc increases rate of photosynthesis as more CO2 can be used to make glucose
• at high enough light intensity/CO2 conc, they no longer increase rate of photosynthesis as they are no longer limiting factors
• increasing light intensity increases rate of photosynthesis as more light energy is absorbed by chlorophyll and used to make glucose
• root hair cell cell membrane prevs cell sap from leaking out, allowing it to have lower water potential than soil solution, water enters via osmosis
• root hair cell contains many mitochondria, aerobic resp in mitochondria releases energy for active transport of ions into cell
• transpirational pull: main suction force that pulls water up the plant from the roots to the leaves
• turgor pressure in leaf mesophyll cells helps support the leaf and keep it firm, allowing leaf to spread out widely to absorb light for photosynthesis
• in strong light, when rate of transpiration exceeds rate of water absorption by roots, cells lose their turgor and become flaccid and the plant wilts
• as water evaporates during transpiration, more water moves out from mesophyll cells to replenish it
• as water is lost from mesophyll cells. w.p of cell sap decreases and becomes lower than neighbouring cells, mesophyll cells draw water from cells deeper inside leaf via osmosis
• cells deeper inside leaf then draw water from xylem via osmosis, creating suction force pulling whole column of water up xylem vessels
• similarity of xylem and phloem?

  both are vascular tissues in plant that function to transport substance through the plant
• sunken stomata lying in grooves contain tiny hairs that trap water vapour diffusing out of stomata, increasing humidity around stomata, reducing rate of transpiration
• w/o wind, water vapour diffuses out of leaf and accumulates outside the stomata, making conc gradient of water vapour inside and outside leaf less steep