topic 9 Flashcards

Question

why are companion cells folded?

Answer 1

to give a large SA for the transport of sucrose

Answer 2

both ways, contrasts with the xylem

Answer 3

to move around products of photosynthesis from sources to sinks

Answer 4

photosynthetic tissues; - mature green leaves - green stems storage organs unloading their stores: - storage tissues in germinating seeds - tap roots of tubers at the start of the growth season

Answer 5

roots growing/absorbing mineral ions parts of the plant with developing food stores (developing fruits, seeds, leaves, tap roots/tubers)§

Answer 6

- it is a non-reducing sugar so will have no immediate reactions with other molecules; glucose is quite reactive so would be taken up by cells on route - osmotic effect - sucrose is more of an efficient energy story (disaccharide more ee than monosaccharide)

Answer 7

1. Sucrose can be loaded into the phloem at sources such as leaves via the symplastic or apoplastic pathway. 2. In the apoplastic pathway, sucrose is co-transported into companion cells along with hydrogen ions. The concentration of sucrose increases in the companion cells so it diffuses into sieve tubes from the companion cells, through plasmodesmata. 3. In the symplastic pathway, sucrose diffuses from cytoplasm to cytoplasm of neighbouring cells. 4. The high solute concentration causes water to move, by osmosis, into the sieve tubes from xylem vessels. 5. The flow of water into the sieve tubes increases the hydrostatic pressure which causes water to flow to areas of lower pressure, such as sinks. Sinks are areas of the plant which don’t synthesise organic molecules, such as the roots. 6. At sinks, sucrose is unloaded from the sieve tubes, which decreases the solute concentration. 7. This leads to water moving back into the xylem vessels by osmosis and as a result, the hydrostatic pressure in the sieve tubes decreases.

Answer 8

sucrose is moved from cells to companion cells and sieve tube elements by diffusion along a concentration gradient, but is moved into companion cells and sieve tube elements by an active process

Answer 9

via the apoplastic pathway

Answer 10

- companion cells have membrane folding for a large SA for transport of sucrose - also have many mitochondria to release the ATP needed for active transport - if these mitochondria are poisoned, translocation in the phloem stops - the pH of the companion cells is higher than the surrounding cells, supporting the idea of a hydrogen pump - the flow of sugars in the phloem is about 10000 times faster than it would be by diffusion alone, suggesting an active process is driving the mass flow

Answer 11

This is because the sieve element cells have no nuclei and fewer organelles (to maximise flow rate)

Answer 12

Plasmodesmata exist between sieve elements and companion cells in relatively large numbers These connect the cytoplasm of the two cells and mediate the symplastic exchange of metabolites

Answer 13

indeterminate growth

Answer 14

undifferentiated cells in the meristems of plants

Answer 15

many plant cells, including some fully differentiated types, have the capacity to generate whole plants (ie the cells are totipotent)

Answer 16

primary meristems are found at the tips of stems and roots (apical meristems) many dicotyledonous plants also develop lateral meristems

Answer 17

mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves

Answer 18

With each division one cell remains in the meristem while the other increases in size and differentiates as it is pushed away from the meristem region

Answer 19

protoderm (gives rise to epidermis), procambium (gives rise to vascular tissue), ground meristem (gives rise to pith)

Answer 20

they control growth in the shoot apex

Answer 21

plant hormones that initiate growth of roots, influence development of fruits and regulate leaf development

Answer 22

indole-3-acetic acid (IAA); control of growth in the shoot apex. When produced by the shoot apical meristem, it promotes growth in the shoot apex via cell elongation and division prevents/inhibits growth in lateral (axillary) buds - apical dominance

Answer 23

synthesised in the apical meristem of the shoot and transported down the stem to stimulate growth

Answer 24

Gibberellins and Cytokinins

Answer 25

- as the shoot apical meristem grows and forms leaves, regions of meristem are left behind at the node - growth here is inhibited by auxin produced by the shoot apical meristem - the further distant a node is from the apical meristem, the lower the concentration of auxin and the less likely that growth in the auxiliary bud will be inhibited by auxin

Answer 26

produced in the root and promote auxiliary bud growth. the relative ratio of cytokinins:auxins determine whether the auxiliary bud will develop

Answer 27

by tropisms (directional growth responses to directional external stimuli_

Answer 28

growth towards light

Answer 29

growth in response to gravitational force

Answer 30

- when light falls on a plant, light energy is absorbed by phototropins (photoreceptor proteins), causing a change in their 3D shape - the altered shape of the phototropins allows them to bind to receptors inside the cell, affecting the expression of certain genes - the affected genes could code for glycoproteins called PIN3 proteins, thought to be involved with the transport of auxin from cell to cell

Answer 31

1. phototropins in the tip detect a greater intensity of light on one side of the stem than the other 2. IAA is transported laterally from the light to the shaded side due to changed expression of PIN3 proteins 3. higher concentrations of IAA on the shaded side cause greater growth on this side, so the stem grows in a curve towards the source of the brighter light

Answer 32

- when a root is placed on its side, auxin will accumulate on the lower side of the plant in response to the force of gravity - higher concentrations of auxin inhibit root cell elongation so the top cells elongate at a higher rate than the bottom cells, causing the root to bend downward

Answer 33

set up concentration gradients of auxin in plant tissue

Answer 34

- cellular organelles called statoliths accumulate on the lower side of cells - this leads to distribution of PIN3 transporter proteins to the bottom of the cell

Answer 35

1. Tissues from the stock plant are sterilized and cut into pieces called explants (for most applications, the least differentiated tissue serves as the source tissue such as a meristem). 2. The explant is placed into sterilized growth media that includes plant hormones. 3. Inclusion of equal proportions of auxin and cytokinin into the media leads to the formation of an undifferentiated mass called a callus. If the growth media contains a ratio of auxin that is greater than ten times the amount of cytokinin, then this is called rooting media and roots develop. If the ratio of auxin to cytokinin is less than 10:1, then this is called shoot media and shoots develop. 4. Once roots and shoots are developed, the cloned plant can be transferred to soil.

Answer 36

When plant tissues are cultured in the laboratory (in vitro) in order to reproduce asexually

Answer 37

- rapid bulking up of new varieties - production of virus-free strains of existing varieties - propagation of orchids and other rare species with desired characteristics

Answer 38

The growing shoots can be continuously divided and separated to form new samples

Answer 39

viruses are transported within a plant from cell to cell through vascular tissue and via plasmodesmata

Answer 40

flowering involves a change in gene expression in the shoot apex

Answer 41

a trigger causes the shift from vegetative phase (young plant) -> reproductive phase, when meristems in the shoot start to produce parts of flowers instead of leaves

Answer 42

the length of light and dark periods in many plants (where length of darkness is what matters)

Answer 43

flower in summer when the nights have become short enough

Answer 44

flower in the autumn when the nights have become long enough

Answer 45

phytochrome (pigment) that can switch between two forms, Pr and Pfr - when Pr absorbs red light of wavelength 660nm it is converted into Pfr - when Pfr absorbs far-red light of wavelength 730nm it is converted into Pr (this is not of great importance as sunlight contains more light of wavelength 660nm so in normal sunlight phytochrome is rapidly converted to Pfr) - Pr is more stable so in darkness Pfr very gradually changes into Pr

Answer 46

Pfr; receptor proteins are present in the cytoplasm to which Pfr but not Pr binds

Answer 47

large amounts of Pfr remain at the end of short nights and bind to the receptor, which then promotes transcription of genes needed for flowering

Answer 48

Pfr inhibits transcription of the flowering time gene (FT gene), preventing flowering; so flowering requires low levels of Pfr (resulting from long nights)

Answer 49

providing additional light in the middle of the night

Answer 50

- nectar-secreting glands attract insects, especially bees - petals are large and colourful, helping insects to find the flower. - sepals protect the flower bud during its development and at night when buds close. - anthers produce pollen, containing the male gametes. - filaments hold the anthers in a position where they are likely to brush pollen onto visiting insects - female part of the flower is called a carpel. It consists of a stigma, style and ovary. The stigma is sticky and will capture pollen from the visiting insect. The stigma is held up by the style. The ovary is located inside a small rounded structure called an ovule.

Answer 51

sexual reproduction in flowering plants depends on the transfer of pollen from the stamen to a stigma of another plant pollinators gain food in the form of nectar; plant gains a means to transfer pollen to another plant.

Answer 52

1. from each pollen grain on the stigma a tube grows down the style to the ovary 2. the pollen tube carries male gametes to fertilise the ovary, which is located inside a small rounded structure called an ovule 3. the fertilised ovule develops into a seed and the ovary develops into a fruit

Answer 53

- reduces competition between offspring and parent - helps to spread the species

Answer 54

Oxygen – for aerobic respiration (the seed requires large amounts of ATP in order to develop) Water – to metabolically activate the seed (triggers the synthesis of gibberellin, which stimulates mitosis and cell division) Temperature and pH – for optimal function of enzymes

Answer 55

- sieve plate with sieve pores - allows for continuous movement - cellulose cell wall - strengthens wall to withstand hydrostatic pressure - no nucleus, vacuole or ribosome - maximise space for translocation - thin cytoplasm - reduces friction to facilitate movement

Answer 56

- nucleus and other organelles present - provides metabolic and genetic support to sieve tube elements, helping w loading and unloading - transport proteins in plasma membrane - moves assimilates into and out of sieve tube elements - large numbers of mitochondria (provide ATP for active transport) - plasmodesmata - allows organic compounds to move from companion cells to sieve tube elements

Answer 57

equation - depends on relative solubility of the pigment - each pigment has a specific Rf value - can be used to identify different pigments

Answer 58

chlorophyll, carotene, xanthophyll

Answer 59

a. aphids tap into phloem with their stylets «to use sap as a food source» b. plants grown in radioactive CO2/14CO2 incorporate it into carbohydrate c. phloem contents/sap/fluid flows through the stylet d. aphid body severed/cut from stylet «after stylet inserted into phloem» e. analyze «sap/fluid exuded from stylet» for solutes/carbohydrates OR radioactive-labelled carbon can be detected «in the phloem sap» f. stylets at different parts of the plant can show sequence/rate of movement

Answer 60

a. increases cell elongation/growth/enlargement OR has effect on rate of mitosis b. changes the pattern of gene expression promotes transcription of some genes c. changes the pH of the extracellular environment/cell wall and increases activity of proton pumps d. breaks cross links/connections between cellulose fibres in cell wall e. increases cell wall plasticity f. «varying» auxin concentrations have different effects in different parts of the plant

topic 9 Flashcards

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