Chapter 9 - Plants as organisms Flashcards
Photosynthesis summary
C02 taken in by leaves and water taken up by roots, chlorophyll traps light energy needed and this energy is used to convert the C02 and water into glucose. Oxygen is released as a by product and some glucose is converted into insoluble starch for storage.
Iodine test on leaves
Starch is identified by the solution turning blue/black in the green patches.
Limiting factors
Anything that stops the rate of photosynthesis above a certain level: lack of light (energy), cold (ineffective enzymes) and lack of carbon dioxide.
Greenhouses and polytunnels
Optimum temperature for enzyme activity, C02 levels increased, artificial lighting extends amount of time plants photosynthesise. Costly but higher yield = more profit
Uses of soluble glucose
Converted to insoluble starch for storage in organs, respiration, converted into fats and oils for storage, to produce cellulose (strengthens cell walls) and to produce proteins.
Venus flytrap
Carnivorous plant, adapted to live in nutrient-poor soil, obtains most of its nutrients from the animals it digests. Obtains nitrates by digesting animal protein.
Plants respire
24 hours a day
Glucose is soluble in
Water but starch is insoluble. I
Stomata
Small holes in leaves that gases (oxygen for respiration and carbon dioxide for photosynthesis) diffuse in and out of. Size of the stomata is controlled by the guard cells around them. Close to prevent wilting.
Waxy cuticle
Waterproof layer that prevents water loss
Leaves
Flat and thin so gases of t have to diffuse far
Root hair cells
Increases surface area of roots for absorption of water and mineral ions.
Layers of tissues in leaves
Upper epidermis
Palisade layer
Spongy layer
Lower epidermis
Has plenty of air spaces and shot diffusion distances for efficient gas diffusion.
Transpiration
Water taken through roots, passed through the plant to leaves, water evaporates and vapour diffuses through stomata.
Transpiration stream
The movement of water through a plant
Evaporation
More rapid in hot dry or windy conditions, plants dehydrate if the rate of evaporation is greater than the water uptake by the roots.
Wilting
Reduces water loss as the leaves collapse and hang down which reduces s.a.
Xylem tissue
Transports water and mineral ions from roots to stem.
Phloem
Carries dissolved sugars from the leaves to the rest of the plant including growing regions and storage organs = translocation.
Phototropism
Plant shoot grow towards the light
Gravitropism
Roots grow down toward gravity.
Hydrotropism
Roots grow towards water.
Auxin
Hormone controlling phototropism and gravitropism.
Roots
More auxins gather on lower side. Grows more on the side with least auxins so bends and grows towards force of gravity, once it has grown down auxins become once again evenly spread.
Shoots
More auxins gather on the lower side, the shoot grows more on the side with the most auxins making it bend and grow up, until the auxins become evenly spread again.
Plant hormones
Used as weed killer and to stimulate root growth.
Cuttings
When cuttings are taken from plants,hormones are used to encourage roots to grow before the cutting is planted.
Problem with plant hormones
If used incorrectly can cause damage to environment such as harming other plants.
Pollination
Anther produces male gametes in pollen grains. Anther is attached to filament to form stamen. Pollen grains carried by wind etc to carpel (female part). Carpel is made of stigma, style and ovary. Pollen grains attach to stigma and pollination occurs when pollen is attached to stigma.
Wind pollinated flowers
Small, light pollen grains, anthers outside of flower, small petals and large stigmas outside petals.
Insect pollinated flowers
Large brightly coloured petals, scent, nectar, large sticky pollen grains to attach to insects and anther and stigma inside flower so insects brush against them when collecting nectar.
Equation
Carbon dioxide + water = glucose + oxygen
Fertilisation
Pollen grains attach to stigma on top of carpel , where ovules are and pollen tube grows through style into ovule. Two male nuclei from pollen grain migrate into ovule to fertilise egg nucleus and endosperm nuclei. Zygote develops into embryo and endosperm forms food store. Endosperm and female tissues give rise to seed, ovary grows into fruit which surrounds the seed.
