Plants Flashcards
The main parts of growing plants are roots, stems and leaves. Draw a plan diagram to show the arrangement of tissues in the stem of a dicotyledonous plant.
5 marks
epidermis shown on the outside with thickness less than 10 % of overall diameter;
cortex labelled between the outer layer of the stem and the vascular bundles;
xylem shown on the inner side of the vascular bundles;
phloem shown on outer side of the vascular bundles;
vascular bundle with some way of indicating the entire structure;
pith shown in centre;
cambium shown between xylem and phloem;
Explain the functions of the different tissues of a leaf.
8 marks
cuticle (produced by epidermis) prevents water loss
epidermis protects cells inside the leaf
stomata (in epidermis) for gas exchange
palisade parenchyma / mesophyll / layer for photosynthesis
spongy parenchyma / mesophyll / layer for photosynthesis
air spaces for diffusion of O2 / CO2 / gases
spongy mesophyll for gas exchange / absorption of CO2
xylem **transports water **/ mineral salts / ions to the leaves
phloem transports products of photosynthesis / sugars (to flowers / new leaves / stem / roots / fruit)
stomata allow transpiration (which helps transport of mineral nutrients)
guard cells open and close stomata
guard cells close stomata to reduce transpiration
Explain the role of auxin in phototropism.
8 marks
auxin is a plant hormone;
produced by the tip of the stem/shoot tip (apical meristem);
it regulates plant growth;
causes transport of hydrogen ions from cytoplasm to cell wall;
decrease in pH / H+ pumping breaks bonds between cell wall fibres;
makes cell walls flexible/extensible/plastic/softens cell walls;
auxin makes cells enlarge/grow;
gene expression also altered by auxin to promote cell growth;
(positive) phototropism is growth towards light;
shoot tip senses direction of (brightest) light;
auxin moved to side of stem with least light/darker side
causes cells on dark side to elongate/cells on dark side grow faster;
Outline the adaptations of plant roots for absorption of mineral ions from the soil.
5 marks
mineral ions are absorbed by active transport;
large surface area;
**branching **(increases surface area);
root hairs;
root hair cells have carrier protein/ion pumps (in their plasma membrane);
(many) mitochondria in root (hair) cells;
to provide ATP for active transport;
connections with fungi in the soil/fungal hyphae;
Describe the process of mineral ion uptake into roots.
5 marks
absorbed by root hairs / through epidermis
root hairs increase the surface area for absorption
uses active transport / uses ATP / uses energy
use of proteins / pumps to move ions across membrane
against concentration gradient / diffusion gradients into cell / root
can enter cell wall space; symplast / be drawn through cell walls /** apoplastic pathway**
selective / only specific ions absorbed
**Describe how water is carried by the transpiration stream. **
7 marks
transpiration is water loss (from plant) by evaporation;
flow of water through xylem from roots to leaves is the transpiration stream;
evaporation from spongy mesophyll cells;
replaced by osmosis from the xylem;
(diffusion of water vapour) through stomata;
water lost replaced from xylem / clear diagram showing movement of water from xylem through cell(s) (walls) to air space;
water pulled out of xylem creates suction/low pressure/tension; transpiration pull results;
water molecules stick together/are cohesive;
due to hydrogen bonding/polarity of water molecules;
xylem vessels are thin (hollow) tubes;
adhesion between water and xylem due to polarity of water molecules;
creates continuous column/transpiration stream;
Explain how abiotic factors affect the rate of transpiration in a terrestrial plant.
8 marks
- less transpiration as (atmospheric) humidity rises; smaller concentration gradient ( of water vapour)
- more transpiration as temperature rises; faster diffusion / more kinetic energy (of water molecules)
-
faster evaporation (due to more latent heat available)
more transpiration as wind (speed) increases; humid air / water vapour blown away from the leaf; increasing the concentration gradient (of water vapour) - more transpiration in the light; due to light causing stomata to open; wider opening with brighter light hence more transpiration.
- CAM plants opposite
narrower stomata with high carbon dioxide concentration hence less transpiration
List three abiotic factors which affect the rate of transpiration in a typical mesophytic plant.
3 marks
light
temperature
wind
humidity
Explain how wind affects the rate of transpiration from a leaf.
5 marks
wind blows air / water vapour away from the leaf
water vapour that has diffused out of the stomata is carried away
low humidity maintained near the leaf without wind air becomes saturated
large water concentration gradient between inside and outside the leaf
rapid diffusion of water vapour therefore rapid transpiration
no effect if the air brought by the wind is already saturated
Outline adaptations of xerophytes.
4 marks
xerophytes are plants that live in dry conditions;
reduced leaves/spines to prevent water loss (by transpiration);
rolled leaves to prevent water loss / stomata on the inside / sunken stomata;
thick waxy cuticle/hairs on leaves to prevent water loss (by transpiration);
reduced stomata to prevent water loss (by transpiration) / stomata on one side of leaf;
deep/widespread roots to obtain more water;
special tissue for storing water;
**take in carbon dioxide at night **/ CAM plant to prevent water loss;
Outline the role of the phloem in the active translocation of biochemicals.
5 marks
living tissue
composed of companion cells / sieve tube members
companion cells involved in** ATP production**
sucrose / amino acids / assimilate /** products of photosynthesis transported**
bi-directional transport
source / leaves to sink / fruits / roots /storage organs / named storage organ
pressure flow hypothesis / movement of water into phloem causes transport
Describe the metabolic events of germination in a starchy seed.
5 marks
absorption of water
(embryo) increases respiration
(embryo) secretes GA to (aleurone layer)
(stimulates) production of amylase
digestion of starch to smaller sugars / maltose
mobilize to tissues / transport of foods / nutrients to embryo
Explain the conditions needed for seed germination.
6 marks
Germination is the process by which a seed emerges from a period of dormancy and begins to sprout
For germination to occur, a seed requires a combination of:
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)
Temperature – seeds require certain temperature conditions in order to sprout (for optimal function of enzymes)
pH – seeds require a suitable soil pH in order to sprout (for optimal function of enzymes)
Additionally, certain plant species may require additional conditions for germination:
Fire – some seeds will only sprout after exposure to intense heat (e.g. after bushfires remove established flora)
Freezing – some seeds will only sprout after periods of intense cold (e.g. in spring, following the winter snows)
Digestion – some seeds require prior animal digestion to erode the seed coat before the seed will sprout
Washing – some seeds may be covered with inhibitors and will only sprout after being washed to remove the inhibitors
Scarification – seeds are more likely to germinate if the seed coat is weakened from physical damage
