4.1-4.13 the structure and function of plants (not definitions) unit 2

name four structures which are found in plant cells but are not found in animal cells

• chloroplasts

• permanent vacuole

• cellulose cell wall

• plastids such as amyloplasts

describe the structure of the permanent vacuole found in plant cells

it contains cell sap surrounded by a membrane known as the tonoplast membrane

give two organelles found in animal cells which are not typically found in plant cells

centrioles and lysosomes

what are bordered pits

unlignified sections of xylem vessels which allow water to move laterally between cells

describe the structure of cellulose

• straight chains of beta glucose joined by beta 1,4 glycosidic bonds

• hydrogen bonding between chains strengthens cellulose

• individual chains pack into microfibrils which themselves pack into macrofibrils which make up cellulose

describe the structure and layout of the stem of vascular plants

• the xylem and phloem are grouped into vascular bundles which run down the length of the stem

• the vascular bundles are surrounded by ground tissue on their sides, the pith is in the centre of the stem and the cortex is on the outside, they are both mostly composed of parenchyma cells

• the cambium strip runs around the stem between the xylem and phloem, it contains dividing cells which can produce the vascular bundles as the plant grows

what does the xylem transport and in which direction

the xylem transports water and minerals up the plants from the roots to shoots

what does the phloem transport and in which direction

cell sap and sugars from source to sink

what is secondary thickening

the lateral growth of the cambium tissue in plants to increase the thickness of the plant stem and vascular tissue

what are the sclerenchyma fibres

a type of supportive tissue found in plants made up of cells with lignified cell walls

how can humans use the properties of plant fibres to create materials

• plant fibres are made of long structural polysaccharide chains

• these are joined and strengthened by many hydrogen bonds which make the fibres tough

• one example of a plant based material is cotton which is made of cellulose fibres and is used to create strong fabrics

describe the structure and function of the vascular system in the stem of dicotyledons

vascular bundles organised around a central pith, xylem on the inside of the bundle to provide support and flexibility, phloem on the outside, cambium is found between the two

relate the structure of the xylem to its function

• long continuous columns made of dead tissue, allowing the transportation of water

• contain bordered pits allowing the sideways movement of water between vessels

• walls impregnated with lignin providing structural support

define translocation

the movement of organic compounds in the phloem from sources to sinks

summarise the mass flow hypothesis of translocation

• sugar loaded into sieve tubes via active transport

• lowers water potential causing water to move in from the xylem

• hydrostatic pressure causes sugars to move towards the sink

give evidence for the mass flow hypothesis

• sap is released when the stem is cut must be pressure in phloem

• sap exuding from the stylet (mouthpart) of an aphid inserted into sieve tubes provides evidence that sugars are carried in the phloem

• there is a higher sucrose concentration in the leaves than the roots

• autoradiographs produced using carbon dioxide labelled with radioactive carbon provide evidence for translocation in the phloem

what is the role of Mg2+ in plants

Mg2+ is used to produce chlorophyll

what is the role of Ca2+ in plants

Ca2+ is used to strengthen cell walls in plants

what is the role of nitrate ions (NO-3) in plants

nitrate ions are used in the synthesis of amino acids which are themselves used to produce proteins

what are the conditions required for bacterial growth

• sufficient nutrients

• an appropriate temperature

• high moisture levels

• high oxygen levels for aerobic bacteria

• a well regulated pH

describe the phases of population growth

• lag phase : period of slow population growth

• log phase : period of rapid population growth in which birth rate exceeds death rate

• stationary phase : period of stability in which population numbers generally remain constant

how can plant based chemicals be used in healthcare

• many plants can provide antimicrobial properties , for example tea tree oil has certain antifungal and antibacterial properties

• lots of plants can have other therapeutic properties, for example poppy stems can be used to extract morphine which is used to extract morphine which is sued as an analgesic to relieve pain

explain how placebos are used in drug testing

• placebos are identical in every way to the drug being tested except they do not contain any active ingredient

• placebos are used to find out whether the drug being tested is actually effective or if any positive effects are actually related to psychological processes

summarise the process of three phased drug testing

• drug tested on healthy individuals to check for side effects

• drug tested on a group of patients

• drug tested on large numbers of patients one group receiving the existing treatment and the other receiving the new treatment