Plant Biology Flashcards
What do the spongy mesophyll cells have?
Large air spaces, some vascular bundles (xylem+phloem)
Which is the main organ for photosynthesis?
Leaf
Where does photosynthesis mainly take place?
In the palisade mesophyll cells
What does the palisade mesophyll cells have?
Many chloroplasts and are located under teh upper epidermis
What feature do the cell walls of mesophyll cells have and what is it needed for?
They are moist and this is used for gas exchange
What does the waxy cuticle do?
Prevents excessive transpiration and also blocks gas exchange
What are stomata and what do they do?
Pores in the epidermis of leaves and stems which allow gas exchange of co2, o2 and water vapour
What is the function of guard cells?
Control the aperture of the stoma
Label the following diagram
Cuticle, Upper epidermis, Vascular bundle, xylem, phloem, air space, lower epidermis, stoma, guard cells, spongy mesophyll, palisade mesophyll
What is transpiration?
The loss of water vapour from the leaves and stems of plants
State how water is lost from a plant
Water evaporates from the moist cell walls of the mesophyll. This makes the air spaces saturated with water vapour and so water vapour diffuses out of the leaf through stomata
How do plants control water losses?
Through stomata using guard cells
What is the transpiration stream?
Replacement of water losses from transpiration by transporting water from the roots to the leaves through xylem vessels
What is a potometer?
A device used to estimate transpiration rates
What does the potometer measure?
The potometer does NOT measure transpiration rate directly. It measures the water uptake. The plant absorbs water to replace the losses. BUT not all water is lost in transpiration. 2% is used in photosynthesis and to maintain turgidity of cells
What is the method used for a potometer?
Distance travelled by an air bubble is recorded every minute and used to indicate the rate of water uptake
What is the experimental method and set up of the potometer?
- A potometer consists of a narrow capillary tube filled with water with a scale to measure the distance travelled by the air bubble.
- A fresh shoot is cut underwater and transferred to apparatus under water to avoid introducing air bubbles
- As plant transpires, it draws water out of the capillary tube to replace losses
- Because the capillary tube is narrow, small losses of water give measurable movements of air bubbles
- Repeat measurements are needed for reliable results
What are the main abiotic factors affecting transpiration rate?
Temperature, humidity, wind speed (light intensity)
Describe the effect of temperature on transpiration
As temp increases, rate of transpiration rate increases because increasing temperature increases the rate of water evaporation from the surface of mesophyll cells, it increases the rate of diffusion of water vapour and decreases the relative humidity outside of the leaf. At v high temperatures, stomata start closing reducing transpiration rate
Describe the effect of humidity on transpiration rate
As atmospheric humidity increases the rate of transpiration decreases because as atm humidity increases the concentration gradient between the air spaces inside the leaf and the air outside decreases so the rate of diffusion of water vapour decreases
Describe the effect of wind speed on transpiration rate
As wind speed increases, transpiration rate increases and this is because the water vapour around the leaf is blown away so the humidity around the leaf decreases thus increasing the conc gradient of water vapour so the diffusion of water vapour increases
Describe the effect of light intensity on transpiration rate
As light intensity increases transpiration rate increases. bc stomata are open with light to allow gas exchange for photosynthesis. Above a certain light intensity increasing the intensity does not affect transpiration bc all stomata are already open (exception: plants with CAM physiology which open stomata at night)
What mineral ions do plants absorb?
Phosphate, nitrate, potassium and magnesium ions
How are plants able to absorb substances?
They absorb mineral ions by active transpiration and this causes water to be absorbed by osmosis
Describe the uptake of mineral ions
Conc of mineral ions in the soil is lower than inside the root so they are absorbed by AT. Ions need to make contact with an appropriate protein pump and this occurs by diffusion or by mass flow when water carrying the ions drains through the soil
What happens as a result of the AT of mineral ions?
The solute concentration becomes higher in the cytoplasm then in the soil’s water and so root cells absorb water by osmosis
Describe the movement of water in the roots
Once the water is in the roots, it travels from the epidermis to the cortex then to the endodermis and inside the xylem vessels
State the two ways water moves in the root
Apoplast route (through cell walls)
Symplast route (through cytoplasm- connected via narrow cytoplasmic connections called plasmodesmata)
What happens at the endodermis?
The Casparian strip blocks the apoplast route and water has to pass through the cytoplasm of the endodermis
What are adaptations of roots for absorption?
- Branching of roots - increased SA
- Root hairs in root epidermal cells- increased SA
- Root hair cells have many mitochondria because they release a lot of ATP to perform AT. Also many pumps for active transport
- Have a symbiotic relationship with a fungus. mutually beneficial- fungus hyphae grow into soil and absorb mineral ions for plant and plant supplies sugars and nutrients to fungus.
What are xerophytes?
Plants that are adapted to grow in dry habitats
Adaptations of cacti?
- Vertical stem to absorb sunlight early and late in the day but not at midday when light is more intense
- Thich waxy cuticle to reduce transpiration
- Spines instead of leaves to reduce SA for transpiration
- Stems with water storage tissue
- CAM physiology- opens stomata during the night than during the day and so the absorbed co2 is stored as malic acid and during the day co2 is released from the malic acid which allows photosynthesis even when the stomata are closed
What are adaptations of Ammophilia Arenaria that grows in sand dunes?
- Rolled leaves and the lower epidermis and stomata on the inside- sunken stomata
- Few stomata
- Hairs on the inside of the folded leaves that stop air movement
- Thick waxy cuticle
- Smaller air spaces in the mesophyll
What are halophytes?
Plants that are specially adapted and thrive in saline soils (high conc of Na+ and Cl-)
What are adaptations of halophytes?
- High concentration of other solutes such as sugars and K+ are maintained in the cytoplasm
- Conc of Na+ and Cl- higher than those of the saline soil can be maintained in the vacuoles
- They get rid of excess Na+ by methods such as AT back into the soil, excretion from special glands and accumulation of the ion in certain leaves and shedding them
- They also have adaptations similar to xerophytes for water conservation
What is the vascular tissue?
It contains vessels that transport materials
What are the two types of vascular tissue?
Xylem and phloem
Where are vascular bundles found?
Leaves, stems and roots
Draw and label the cross section of a dicotyledonous plant’s stem
Epidermis, Cortex, Xylem, Phloem, Vascular bundle, Cambium and Pith
Draw and label the cross section of a dicot root
Endodermis, Cortex, Epidermis, Root hair, Xylem, Phloem, Vascular bundle
What is the xylem?
A tissue in plants that transports water and minerals and provides support
What is the main route for water in floering plants?
Xylem vessels
Describe the movement of water in xylem vessels
One direction from roots to leaves and is passive
Describe how the transpiration stream works
When water evaporates from the mesophyll cells in transpiration, adhesion between water and cellulose in leaf cell walls causes water to be drawn from the nearest xylem vessel. This reduces pressure in the xylem near the leaves and generates tension forces in the leaves. The tension generated in the leaves is transmitted through water due to cohesion all the way down the xylem vessels to the roots. This is the transpiration pull and causes water to move up against gravity.
What is cohesion?
Water molecules stick to each other because they are polar and form hydrogen bonds between them o water columns rarely break
What is adhesion?
Water is polar so it adheres to cellulose which is also water/hydrophilic
Describe the structure of xylem
- Long tubes that develop from columns of cells that break down their end walls, plasma membranes and cell contents -non living
- Continuous tubes and their lumen is filled with sap.
- Side walls of xylems are strong bc at times of max transpiration the pressure inside the vessel is v low and the walls need to be strong to prevent inward collapse
- Cell walls have pores called pits to conduct water out of xylem vessels and into cells walls of adjacent leaf cells
What is the wall of xylem made out of?
Cellulose and it is thickened with lignin. The thickenings might be helical or annular
Draw the primary xylem vessel and label it.
Lumen, pit, no plasma membrane, helical lignin
Describe the capillary tubing model to test water transport in xylem
Used to demonstrate cohesive and adhesive properties of water
- If a capillary tube is dipped into water, water rises up against gravity this is bc of adhesion of water with glass walls and cohesion of water
- The thinner the tube the higher the liquid rises
- Water adheres to the glass, so the meniscus is concave
Describe the filter paper model to test water transport in xylem
Used to model the movement of water up the xylem vessels and that water is drawn out of the xylem and into the leaf
- Filter paper absorbs water due to adhesive and cohesive properties
- When placed perpendicularly to water source, the water rises up against gravity
- Both paper and cell wall composed of cellulose
Describe the evaporation of water can cause tension model to test water transport
Porous pots are semi-permeable containers
It is similar to leaf cell wall as water adheres to it and there are many pores
Loss of water from the surface of the pot is similar to the evaporative water loss that occurs in the leaves
If attached to airtight seal to a tube, the water loss creates negative pressure that draws more liquid
What is the function of the phloem?
It is a tissue in plants that transports organic compounds such as sugars and amino acids
What is translocation?
The transport of organic solutes in the plant
Describe translocation properties
Active process and is two direction
Where does translocation take place?
In phloem sieve tubes and the viscous fluid of the phloem is called sap
What are sources and sinks?
Sources= Parts of a plant where organic compounds are synthesised and loaded in phloem sieve tubes by AT
Sinks= Parts of the plant where organic compounds are delivered/ unloaded from phloem sieve tubes for use or storage
What is the main solute carried by phloem sieve tubes?
Sucrose
Describe how sucrose is able to be loaded into the phloem
Through AT and Co-transport
- Protons are pumped out of the phloem cells by AT to create a proton gradient. Co- transporter proteins in the membrane use this gradient to co-transport into cell sucrose together with protons
- Some sucrose is loaded into phloem sieve tubes by this process
- In some species, to speed up, sucrose also travels between adjacent cells via plasmodesmata
Describe transport in phloem sieve tubes
- Hydrostatic pressure is pressure in a liquid
- The incompressibility of water allows transport along hydrostatic pressure gradients
- At source, there is high solute conc. in phloem sieve tubes leading to uptake of water from xylem by osmosis. Bc of incompressibility, hydrostatic pressure increases
- At sink, solutes are unloaded so there is low solute conc in the phloem sieve tubes leading to exit of water to xylem by osmosis an so hydrostatic pressure decreases
- therefore sap travels from high pressure to low pressure (source to sink)
What are the main cell types in phloem tissue?
Phloem sieve tubes and companion cells
What are companion cells?
Connected with sieve tube cells via plasmodesmata and are involved in ATP production so they have mitochondria. Companion cells provide metabolic support for sieve tube cells and facilitate the loading and unloading of organic compounds
Describe the structure of the phloem sieve tubes
- Develop from columns of sieve tube cells that break down their nuclei and most of their cytoplasmic organelles but maintain plasma membrane and are alive- does not obstruct flow of sap
- Individual sieve tube cells are separated by perforated walls called sieve plates that strengthen sieve tube and has pores that allow sap to pass through in either direction
- Cell wall resists high pressure inside the sieve tube
- Plasma membrane holds sap inside the active tubes and has pumps to load and unload sucrose
Describe how you can measure phloem transport rates
- Using aphid stylets and radioactively- labelled co2
- Aphids are insects with long piercing mouthparts called stylets which feed on phloem sap
- Aphids insert their stylets into stems and push it inwards until the stylet pierces a sieve tube thus causing sap to push out
- To collect phloem sap, aphids are placed at plant’s length adn once they start feeding they are cut off from the stylet. The sap continues to emerge
- Radioactive co2 is supplied to photosynthesising plant and so radioactive sucrose is made and loaded into phloem
- Time taken for radioactive sucrose to emerge from severed aphid stylets at diff distances from leaf can be used to give measure to rate of movement of phloem sap
What is this?
Monocot root
What is this
Monocot stem
What is growth in a plant?
Indeterminate- ie plants continue to grow throughout their life: stem and roots continuously increase in length and parts
What is growth due?
Cell division and cell enlargement
What allows indeterminate growth in plants?
Undifferentiated cells in meristems
Where does growth take place?
Meristems
What are meristems?
Composed undifferentiated cells that are repeatedly undergoing cell division (mitosis and cytokinesis) to produce more cells
Where do flowering plants have meristems?
At the apex- tip- of the root and shoot called apical meristems and these give rise to the primary tissues that increase the plant’s length
What do many dicotyledonous plants have?
Later meristems which give rise to the secondary tissues that increase the plant’s width
Describe the growth of the shoot apex
The cells in the shoot apical meristem undergo cell division repeatedly to generate the cells needed for stem extension and leaf development and with each division one cell remains in the meristem and continues to divide while the other is displaced to the edge of the meristem. Cells at the edge stop dividing and undergo growth and differentiation to become either stem or leaf tissue.
How are leaves initiated?
As small bumps at the side of the apical dome called leaf primordial. And this develops into mature leaves through cell division and rapid growth
What are axillary buds?
Embryonic shoots that form at the junction, or node, of the stem and the base of the leaf. As the shoot grows, regions of meristem are left behind at the node and may form shoot immediately or remain dormant for some time and shoot later on.
Label this
Leaf primordial, region of growth, leaf, axillary bud, meristem (check notes)
What are tropisms?
The directional growth responses to directional stimuli in plants
What is phototropism/ gravitropism?
Phototropism- growth towards light
Gravitropism- growth in response to gravity
What is the main hormone of plants?
Auxins that are produced in the tips of roots and stems and the most abundunant auxin is IAA
Give an overview of how auxin controls growth in shoot apex
- The plant hormone auxin acts as a growth promoter at the shoot apex
- Auxin controls phototropism at the shoot apex
- Auxins are synthesised in the apical meristem of the shoot and are transported laterally from the side with light to the more shaded side
- Their main effect is to cause growth by changing the pattern of gene expression and promoting cell elongation
Give in detail of how auxin controls plant growth
- Auxins are synthesised in the shoot apical meristem
- Protein photoreceptors in the tip called phototropins absorb light. When they detect differences in light intensity, they trigger the asymmetric distribution of auxin efflux pumps
- Auxin efflux pumps are proteins that carry out AT of auxins from cell to cell
- Due to asymmetric distribution of auxin efflux pumps, a conc gradient of auxin is established from lower auxin conc on the lighter side to higher auxin conc on the shadier side
- Auxin influences cell growth rates by changing the pattern of gene expression
- Auxin binds with to an auxin receptor which in turn promotes transcription of specific genes
- Expression of these genes causes secretion of hydrogen ions into cell walls decreasing pH
- This loosens the connections between cellulose fibres thus increasing flexibility of cell walls and allowing cell expansion
- Thus higher conc of auxin on the shadier side cause greater cell elongation on this side. Stem grows in a curve towards the source of light.
Describe how auxin controls gravitropism
In the roots auxin inhibits cell elongation and thus limits growth. If a root is placed on its side, due to gravity organelles called statoliths accumulate on the lower side of cells. So distribution of auxin efflux pumps and auxin at the bottom of the cells. Higher conc of auxin inhibit root elongation so the top cells elongate at a higher rate than bottom cells causing the root to bend downwards
How can plants be cloned?
Using stem cuttings or micropropagation
What is micropropagation?
An in vitro procedure that produces large numbers of identical plants with a desirable characteristic and this depends on the ability of plant tissues to differentiate into any functional plant part
List the steps of micropropagation
- Aseptic technique is followed
- Meristem serves as the source
- Stock plant with a desirable feature is identified
- Tissues called explants are cut into pieces and sterilised
- Explants are placed in sterilised growth medium that has a high concentration of auxin to stimulate growth and division. An undifferentiated mass is called a callus
- The callus is transferred to growth medium of lower concentration of auxin and high concentration of cytokinin- stimulates root and shoot development
- Gibberellin is added to increase shoot growth and prevent dormancy
- Once roots and shoots are developed the cloned plant is transferred to soil
What are advantages of micropropagation?
- New varieties can be bulked up quickly
- Virus- free strains can be produced bc the apical meristem is often free of viruses
- Large numbers of endangered species can be produced
How do plants reproduce?
Sexually or asexually
What is the reproductive organ in flowering plants?
THe flower
How are flowers produced?
Produced by the shoot apical meristem
Draw a half view of an animal- pollinated flower and label it.
Check notes.
What are petals?
Large and colourful to help the insect find the flower
What are sepals?
Protect teh bud during its development and when it closes
What is the nectary?
Glands which secrete nectar to attract insects
What are the anthers?
Produce pollen containing the male gametes
What are the filaments?
Hold the anthers in a position where they are likely to brush pollen onto visiting insects
What is the stigma?
Is sticky to capture pollen from visiting insects
What is the ovary?
Contains ovules, which contain the female gametes
What is the carpel?
Flower’s female part
What is the stamen?
The flower’s male parts
What is the stimulus that causes the plant to switch to its reproductive phase?
The change in the length of light and dark periods
What are short- day plants?
Flower when the days are short (autumn)- Night length is longer than critical period
What are long- day plants?
Only flower when the days are long(summer)- Night length is shorter than critical period
What does the switch in a change in length of light and dark periods involve?
A change in gene expression
Describe in detail flowering.
- Plants contain a pigment called phytochrome which is used to measure the length of dark periods
- Phytochrome switches between PR and PFR
- In sunlight, PR is rapidly converted to PFR (Absorbs red light)
- In darkness, PFR gradually converts into PR (Absorbs far- red light)
- PFR is the active form of phytochrome. It leads to the expression of the FT gene which in turn activates many genes that transform the leaf producing apical meristem into a flower- producing meristem.
- In long- day plants, enough PFR remains at the end of short nights to stimulate flowering so PFR acts as a promoter of flowering in long day plants and hence flowering requires high levels of PFR
- In short day plants, at the end of long nights enough PFR has been converted to PR to allow flowering to occur. PFR acts as an inhibitor in flowering in short day plants and hence flowering requires low levels of PFR .
What is flowering forcing?
A procedure used to get flowers to bloom out of season by manipulating the lengths of days and nights.
What are the four procedure that ensure success in sexual reproduction?
Meiosis
Pollination
Fertilisation
Seed dispersal
What is meiosis?
The cell division that generates the haploid male and female gametes
What is pollination?
The transfer of pollen from an anther to the stigma of the flower
How does fertilisation occur?
Pollen grains that land on the stigma germinate and a pollen tube grows down the style to the ovary. The pollen tube delivers the male gametes to ovules.
What is fertilisation?
The fusion of a male gamete from pollen with a female gamete inside the ovule to produce a zygote and the fertilised ovules develop into seeds and ovaries turn into fruits.
What is seed dispersal?
The spreading of seeds away from the parent plant to sites where they can germinate and grow without competing with their parent
What are some seed dispersal mechanisms?
- Wind
- Water
- Fruit ingested by mammals and egested somewhere else
- Coats of animals
What is mutualistic relationship?
There is a mutualistic relationship between plant and insects because both species benefit
What does a seed contain?
An embryo plant and food reserves inside a protective seed coat
Draw an annotated diagram of the internal structure of seeds and state their funtions
- Cotyledon- contains the food stores, which are used by the embryo for germination
- Plumule- The embryonic shoot
- Radicle- The embryonic root
- Testa- The outer seed coat that protects the embryonic plant
- Micropyle- A small pore in the testa that allows for the passage of water
What is germination?
The early growth of a young plant from a seed
What are the main factors needed for germination?
- Water (activate metabolism)
- Oxygen (aerobic cell respiration)
- Warmth (optimal enzyme activity)
- Optimal pH (optimal enzyme activity)
What are stages in germination?
- Absorption of water to metabolically activate the seed
- Hormone gibberellin is synthesised. Stimulates cell division on the embryo
- Gibberellin stimulates the production of amylase. Amylase breaks down starch in food reserves into maltose. Maltose is broken down to glucose which is used for cell respiration and to be polymerised to build cell walls.
- Once the seed is metabolically activated, the testa ruptures and the radicle grows into the ground to absorb minerals. Then the plumule with its first leaves emerges.
