Biology - Plant Biology

transpiration

loss of water from leaves and stems of plants

xylem vessels

____ transport water through the plant, due to its cohesive properties

mesophyll

water is heated at the _____ by sunlight and becomes vapour, then transpires out of the leaf through the stomata-pores

negative pressure and a transpiration pull

loss of water from vapour leaving via stomata pores generates _____ on water molecules in the xylem

more water is drawn into the leaf and roots

as a result of transpiration pull, ___

this has a knock on effect through the plant

cohesion between water molecules means that when transpiration pull occurs, ____

transpiration stream, water uptake

higher rates of transpiration lead to a faster __ and higher rates of ____

cohesion tension theory

____ explains how water flows upward (against gravity) through plants' xylem

cohesion

____ between water molecules allows water to be transported together

adhesion

____ allows water to stick to the xylem vessel and hence move upwards

roots \[high\], leafs \[low\]

after negative pressure is created, concentration gradient is formed moving water from __ to __

* CO2 uptake low, water loss low
* low pressure in cytoplasm
* guard cells flaccid

effects of a closed stomata

* CO2 uptake high, water loss high
* high pressure in cytoplasm
* guard cells turgid

effects of an open stomata

* sunlight/high photosynthesis
* reduced CO2 concentration

stomata opens by:

* Water shortage
* darkness

stomata closes by:

factors affecting transpiration

* Higher wind → lower humidity → higher transpiration
* higher humidity → lower transpiration
* higher temp → higher transpiration
* higher light intensity → higher transpiration

* No cytoplasm
* Strong walls (lignin)
* End to end cells

Xylem cells structure and function

xylem vessels inside, phloem cells outside, cambium seperating

tissue plan diagram in a dicotyledon stem

xerophytes

survive in dry conditions by reducing transpiration

Life cycle adaptations

* perennial plants bloom in wet seasons
* dormant seeds can survive for many years until conditions are ideal for growth

Metabolic adaptations

in CAM plants CO2 is absorbed at night and stored a C4 compounds, during the day, photosynthesis can occur with the stomata closed by using these carbon stores

Physical adaptations

* fewer leaves or stomata
* rolled leaves or spines
* stomata in pits with hairs
* deeper roots to reach water
* waxy cuticle reduces evaporation

roots, SA

Plants take up water and essential minerals via their ___ and thus need a large ____ to optimise this

root epidermis, root hairs

the __________ may have extensions called ____ which increase SA for mineral and water absorption

Minerals

_____ are initially actively transported into roots through use of ATP

sieve element cells

transport water and solutes

* redcued cytoplasm
* no nucleus, ribosome or vacuole

structure and function of sieve element cells

Companion cells

are “life support” for sieve element cells as they perform certain metabolic functions for sieve elements

Parenchyma

act as packing material between other cell types and helps transfer materials to the sieve elements and companion cells

Fibres of sclerenchyma

provides structural support for the plant

* Rigid cell walls
* Connected cells
* Pores in sieve plates (transport between sieve element cells)

structure and function of phloem sieve tubes

Active translocation

* movement of phloem sap (sugars) requires energy
* plants produce their own carbs in the leaves through photosynthesis
* for the plant to grow and reproduce, this food needs to be transported to the tissues that need it (also true for proteins and amino acids)

Source

site of production or storage

sink

destination/site of use

source of sugars

green leaves and stems

sink for sugars

growing roots and stem roots

* for flowering and reproduction

source of amino acids

roots, tubers

sink of amino acids

growing roots and stem developing leaves, fruits

* for flowering and reproduction

sucrose

___ is actively transported into the phloem

H+ ions are actively transported out of phloem cell

1st step of actively transported sucrose into phloem

High H+ ion gradient builds up outside phloem cell

2nd step of actively transported sucrose into phloem

H+ ions flow back into phloem cell, energy released is used to co-transport sucrose into phloem cell

3rd step of actively transported sucrose into phloem

Hydrostatic pressure

pressure of water before it moves

low water concentration, therefore water diffuses from xylem to phloem by osmosis

High sucrose concentration as a result of active translocation consequently means ___

1. water is incompressible
2. rigid walls of phloem

2 factors that cause a build up of hydrostatic pressure

water and solutes flow down the concentration gradient from the source to the sink where pressure is relatively low

Due to the build up of hydrostatic pressure

active unloading of sucrose occurs, and water flows back to xylem through osmosis

When solutes and water reach the sink ___

Aphids

groups of insects that evolved the ability to ffed primarily on the plant sap

stylet

Aphids possess a ____ that can extract sap. High pressure inside sieve tube pushes sap into the aphids via the ____

Using aphids to measure rate of phloem transport

1. plant grown and 1 leaf is exposed to 14CO2
2. 14CO2 is converted into sucrose during photosynthesis
3. aphids feed on plant and stylet is severed
4. phloem is analysed for 14C content which can be used to calculate translocation rate

1. rate of photosynthesis
2. rate of cell respiration
3. rate of transpiration
4. diameter of sieve tubes

Factors affecting translocation rate

* determined mainly by concentration of dissolved sugars in phloem

Apical meristem

found at the terminal bud of the stem and the root tip

indiscriminate growth: adding size/length to the plant

apical meristems type of growth

axillary bud

* at each section of growth, an _____ is left behind,
* this is inactive meristem tissue, until flowering or growth occurs and the hormonal inhibitor is removed

Meristems

* regions of undifferentiated cells (like stem cells in animals)
* plants can only grow at the ______
* these can be apical (root or stem tip) or lateral (thickening layers of cambium)

1. Cell enlargement
2. increase in cell numbers

growth of a multicellular organism such as a plant can only occur via 1 or a combination of these things:

lateral meristem

* as plants grow taller, they need extra support to support the increased mass
* growth results in extra (secondary) xylem growth in a ring inside the cambium, phloem grows as well

bark

cork cambium produces cork which we know as _____

* result of lateral meristem growth

Hormones

molecules produced by one part of organism and transported to another, affecting physiological activity, such as growth or metabolism

auxins function in plants

* root and shoot growth
* flowering
* fruit development
* leaf development
* wound response

auxin concentration

depending on _______ it can either promote or inhibit growth

tropisms

plants responses to directional external stimuli

* can be positive (towards stimuli) or negative (away from stimuli)

phototropism

* example of positive tropism
* plant growth towards light

auxins

plant growth is regulated by ___

lengthening cells

auxins promote growth by ______

coleoptile

auxins are produced in the _____, a protective sheath around the emerging root or shoot

even (vertical) growth

under normal conditions, auxin is distributed evenly along the shoot, causing _____

photoreceptors, opposite

if ________ in the coleoptile detect a light stimulus from one direction, auxin is moved to the ____ side of the growing shoot

uneven distribution of auxin

The ___________ causes increased growth on one side, plant grows towards the light

Gravitropism

response to gravity, can be positive or negative

auxin

_____ affects gene expression in shoots

auxin receptor

cells contain an ________ which when auxin binds to, transcription of certain genes occurs

H+ ions, loosening connection between cellulose fibres

expression of these genes as a result of auxin binding causes secretion of ____ into cell walls, ________ allowing cell expansion

inhibition of growth

Auxin can also lead to the ________ as seen in roots

1. diffusion
2. influx transporter proteins

auxin can enter the cell by ___

Efflux transporter proteins

auxin can exit cell by ____

factors affecting transporter proteins and hence direction in which auxin can move

1. location of transporter proteins (can change as plasma membrane is fluid)
2. transporter proteins can be activated and/or inhibited by stimuli

micropropagation

used to produce large numbers of identical plants from stock plants

micropropagation steps

1. tissues sample scraped from parent plant
2. tissues samples placed in sterile agar growth medium containing nutrients and auxins
3. samples develop into tiny plantlets
4. plantlets planted into compost

virus-free plants

propagating plants from sterilised vascular tissue produces _____

orchids

example of micropropagation in plants

* difficult to get ____ to breed sexually and maintain desired traits

1. pollination
2. fertilisation
3. seed dispersal

reproduction in angiosperms


1. pollen carried from anther of one flower to stigma of another
2. pollen tube grows down stigma to the ovary, through the style, pollen is delivered to ovum
3. once seed has developed into the ovule, it is ready for dispersal

structure/function of flower

petal

attracts pollinators

stigma

pollen landing site

style

pollen tube grows down ____ from stigma to ovary

ovary

contains ovules

* contains egg nuclei and develops into seeds when fertilised

anther

contains pollen

filament

supports anther

sepals

cover/protect developing flowers

male parts on flower

Anther, Filament

female parts on flower

Ovary, Style, Stigma

cross pollination

transfer of pollen between flowers

* leads to grater variation in next generation

wind or water, animals

some flowering plants rely on _______ for pollination, but most use _____ to transfer pollen

Mutualism

close association where 2 organisms benefit


1. animal gets food
2. flower gets pollination

floral initiation

* caused by the growth and differentiation of apical meristems due to changes in gene expression

photoperiod (day length)

Causes of changes in gene expression leading to floral initiation vary but most common is ___

Control of flowering

* flowers should only bloom when suitable pollinator is abundant
* this is controlled by photoperiodism

photoperiodism

response of an organism to changes in day-length

phytochromes

leaf pigments which can be used to ‘measure’ the length of the night