Topic 4 Wood

Question 1

Plant cell ultrastructure

Answer 1

• cell wall
• cell membrane
• cytoplasm
• nucleus
• nucleolus
• ribosomes
• chloroplasts
• vacuole (tonoplast)
• amyloplasts
• rER
• sER
• Golgi apparatus
• mitochondria

Question 2

Cell wall

Answer 2

• made of cellulose
• provide strength and support to regular shape
• there are pores within the walls called plasmodesmata which connect two cells together by their cytoplasm enabling exchange and transport of substances

Question 3

Vacuole

Answer 3

• fluid filled space in the cytoplasm
• surrounded by a single membrane (tonoplast)
• permanent in plant cells
• contains water, ions, sugars (cell sap)
• can also be used for storage
• keeps cells turgid

Question 4

Amyloplasts

Answer 4

• organelles that store amylopectin
• has a double membrane
• amylopectin sometimes shown as concentric rings
• amylopectin can be broken down into alpha glucose and used to provide energy (is an energy store) for the plant cell

Question 5

Chloroplasts

Answer 5

• found in photosynthetic cells
• site of photosynthesis (thylakoid membranes)
• have a double membrane and many internal membranes
• fluid filled interior called the stroma
• contain their own DNA (typically circular)

Question 6

Chloroplast structure

Answer 6

the thylakoid space has thylakoid membranes and stacks of these are called grana (granuum) in a fluid called the stroma

Question 7

Plant cells build columns and tubes from specialised cells which are stiffened…

Answer 7

by another polymer called lignin

Question 8

What is cellulose?

Answer 8

is a polymer of β glucose which forms during a condensation reaction creating glycosidic links

Question 9

How are cell walls made strong but flexible?

Answer 9

the cellulose microfibrils are laid down at different angles

Question 10

Within a cell wall there are…

Answer 10

cellulose microfibrils

Question 11

What is the glue holding the microfibrils made up of?

Answer 11

pectins and hemicelluloses

Question 12

Summary of cellulose

Answer 12

• polymer of β glucose
• unbranched, straight chains
• alternating molecules are flipped 180° allowing it to make a polymer chain
• 1,4 glycosidic bonds formed through a condensation reaction
• hydrogen bonds join cellulose chains together making bundles of fibres called microfibrils
• microfibrils are laid at angles for strength
• high tensile strength
• permeable to water and gases

Question 13

Plasmodesmata

Answer 13

cytoplasmic links between adjacent plant cells (holes in cell walls; both the primary and secondary aren’t there)

Question 14

Vascular bundle

Answer 14

xylem, phloem, schlerenchyma

Question 15

How do phloem sieve tubes form?

Answer 15

• cells elongate and lose cytoplasm, nucleus and most other organelles
• the ends don’t break down completely but form sieve plates between cells
• next to each phloem cell is a companion cell which keeps the phloem cell alive
• it is metabolically active and is used in moving photosynthesis products up and down the plant

Question 16

What is transported in translocation?

Answer 16

• sucrose
• hormones
• amino acids
• minerals

Question 17

Phloem transports… (where to where)

Answer 17

substances made in the leaves to other parts of the plant

Question 18

Lignification

Answer 18

• deposit lignin into cell walls - makes it woody

- restricts entry of water and solutes into cell so they die

Question 19

Schlerenchyma

Answer 19

• long elongated hollow cells
• dead cells
• closed ends so not involved in water transportation
• lignin in walls for strength
• thick walls relative to lumen size
• bundles or cylinders

Question 20

Why do phloem sieve tubes need to be metabolically active?

Answer 20

for active transport

Question 21

What is translocation?

Answer 21

the movement of nutrients around a plant (can refer to minerals dissolved in water which are transported in the xylem but generally refers to sugars, amino acids and other organic molecules)

Question 22

Features of translocation

Answer 22

• it is bi-directional (goes both directions)
• it is an active process requiring energy
• goes from source –> sink

Question 23

What is transported in the phloem and how?

Answer 23

amino acids, sucrose, hormones, minerals all by translocation

Question 24

Another name for flowering plants

Answer 24

angiosperms

Question 25

Angiosperms: monocotyledons

Answer 25

- embryos have one seed leaf - leaves have parallel veins - rarely grow large - flowers in multiples of 3

Question 26

Angiosperms: dicotyledons

Answer 26

- embryos have two seed leaves - leaves have a network of veins - can grow large by producing wood (lignin) - flowers in multiples of 4/5

Question 27

Transpiration

Answer 27

the loss of water from plant leaves (through the stomata)

Question 28

Features of water

Answer 28

- is dipolar (oxygen negative, hydrogen positive) - hydrogen bonds occur between two water molecules (more of these makes it stable) - is an effective solvent - has a large specific heat capacity

Question 29

Xylem

Answer 29

are dead, hollow, lignified and have pits which allow movement of water and ions between the xylem and phloem

Question 30

Cohesion (water)

Answer 30

water molecules 'stick' together which holds up the column of water; positive and negative ends cohere so as some molecules leave the plant others are pulled up behind them

Question 31

Adhesion (water)

Answer 31

water molecules 'adhering' to something else; in the xylem water adheres to the walls which helps the water move upwards resisting gravity

Question 32

How would you investigate transpiration

Answer 32

-using a potometer -cut stem underwater -seal in potometer keeping underwater so no air bubbles -bubble moves representing volume lost affecting it air movement doesn't, humidity doesn't, light increases

Question 33

Xerophytes

Answer 33

plants that have evolved to reduce transpiration rates

Question 34

Reducing water loss adaptations

Answer 34

- waxy cuticle - stomata on underside of leaves --> no direct sunlight - stomata close at night - deciduous plants lose leaves in winter

Question 35

Water flow is...

Answer 35

unidirectional (if one part is damaged the whole chain falls)

Question 36

Mass flow in plants

Answer 36

water moving through the xylem is mass flow for inorganic ions - movement down a concentration gradient (are taking in at roots and needed elsewhere)

Question 37

Plants primary cell wall

Answer 37

- cellulose microfibrils are all oriented in a similar direction which means it can elongate and allows further growth - is fully permeable with no lignin

Question 38

Plants secondary cell wall

Answer 38

- cellulose microfibrils are laid down at different angles | - lignin may be laid down as will (lignin is impermeable to water)

Question 39

Middle lamella

Answer 39

region between cell walls of adjacent plant cells which is made of calcium pectates --> glues cells together

Question 40

Human uses of xylem and schlerenchyma

Answer 40

support --> fibres e.g. fabric and ropes

Question 41

Human uses of chemical defences

Answer 41

antibacterial --> medicines, cosmetics, pesticides

Question 42

Human uses of seeds

Answer 42

food starch based products

Question 43

Mineral ions

Answer 43

are actively transported into root cells - this needs ATP as its going against the concentration gradient

Question 44

Lack of mineral ions =

Answer 44

deficiency symptoms

Question 45

Magnesium ions

Answer 45

- part of the chlorophyll molecule which is used in photosynthesis (absorbs sunlight, activates enzymes) - if lacking yellow leaves will be seen

Question 46

Nitrate ions

Answer 46

- used in amino acids which make proteins and allows plant growth - if lacking yellow leaves and stunted growth

Question 47

Calcium ions

Answer 47

- used in respiration and for growth also is in pectate in cell walls so cells won't be able to stick together and will affect membrane permeability - if lacking plant will have stunted growth

Question 48

Pits

Answer 48

secondary cell wall is absent