plants
cuticle
waxy coating protection from excess absorption of lights and evaporation of water
epidermis layer
allows light to get to the mesophyll layer (spongy and palisade) where the majority of photosynthesis happens
guard cells
create opening around stomata, o2 and co2 exchange and transpiration of water
parenchyma mesophyll cells
location of photosynthesis. The palisade mesophyll is a densely packed region of cylindrical cells in the upper portion of the leaf (numerous chloroplasts and receive maximum sunlight). The spongy mesophyll are loosely packed cells located below the palisade and above the stomata (few chloroplasts and many air spaces - SA for gas exchange).
veins
enclose the fluid transport tubes called xylem (moves water and minerals) and phloem (moves carbohydrates). They are located centrally within a leaf to provide access to all layers of the cell. Xylem has larger openings, while phloem has smaller ones
leaves
the photosynthetic organs of plants
what is stomatal density?
the number of stomata per unit area of leaf surface.
stomatal density formula
mean number of stomata / area of field of view (mm2)
Stomatal density technique (epidermis)
sample of epidermis is peeled off the leaf. The leaf can be folded to break the tissues apart from the lower epidermis so it can be peeled off of the leaf and torn in half to separate epidermis layers. The epidermis is then mounted in water on a microscope slide and examined
stomatal density technique (nail varnish)
only works if the leaf is non-hair and smooth. Nail varnish is painted onto a small area of the epidermis. When dry, the nail varnish is peeled off and mounted on a microscope. The varnish forms a cast of the leaf surface with margins of cells and stomata visible.
Where are vascular bundles in dicotyledons?
they are organized in rings around the stem
where are vascular bundlles in monocotyledon?
scattered out throughout the stem
what is a tissue plan diagram?
a map where the different types of tissue can be found, a drawing of each individual cell is not needed
cortex - dicotyledon
an unspecialized cell layer that sometimes stores food reserves. It makes up the majority of the plant
tip - dicotyledon
the xylem is the vascular tissue that is always oriented towards the center in both types of plants
vascular cambium - dicotyledon
a layer of cells that constantly produce new xylem and phloem
tissue distribution (phloem and xylem) in dicotyledon root
xylem vessels are arranged in the form of a cross, while phloem are arranged throughout the whole cylinder.
endodermis - dicotyledon root
a layer of cells that surround the vascular tissue and force waer to pass through the cells instead of inbetween
central region - dicotyledon root
called the stele and is surroundded by an endodermis with a casparian strip (controls water transport)
pericycle/cambium - dicotyledon root
provides strength and is responsible for the development of lateral roots
capillary action
caused by evaporation of water molecules from the leaf mesophyll cells. The only thing required is enough thermal energy to break hydrogen bonds
adhesion (roots to leaves)
in the form of hydrogen bonds between the water and hydrophilic cellulose of the plant cell walls
cohesion (root to leaf)
between water molecules, which forms a continuous column of water and allows pulling of water upwards in xylem vessels. It generates tensions, which are transmitted from leaves to roots.
xylem vessels (transpiration, root to leaf)
xylem sap (water and low concentrations of K+ and Cl-) are inside the xylem vessels. Water diffuses out of mesophyll cells into air spaces through the nearest vein and leaves through the stomata.
osmosis (transpiration, root to leaf)
water enters the root hair cells by osmosis. There is a low concentration of water in the root hair cells compared to the soil water, causing water to move down the concentration gradient and enter the root hair cells.
epidermis extensions (transpiration)
may have extensions called root hairs or lateral branches in taproots, which increase surface area for mineral and water absorption
mineral uptake into the soil
soil contains negatively charged clay particles to which positively charged mineral ions attach. Minerals that need to be taken up include mg2+ (for chlorophyll), nitrates (for amino acids), na+, k+ and po43-. Mineral ions can diffuse passively and actively
Active transport mineral ions from soils
root cells contain proton pumps that actively expel H+ ions (from vacuole) into the surrounding soil. The H+ ions displace the positively charged mineral ions from the clay, allowing them to diffuse into the root along a gradient. Negatively charged mineral ions bind to the H+ ions and be reabsorbed along with the proton.
What apoplast pathway
the mass flow of water through interconnecting free spaces between cellulose fibres of the plant cell wall avoiding the living content of the cell. It is the most efficient pathway
what is the symplast pathway?
the diffusion through the cytoplasm of cells and small openings in the cell wall called plasmodesmata. It is not very significant, since the organelles cause resistance to the flow of water.
vacuole to vacuole pathway
pathway of osmosis driven by a gradient in osmotic pressure caused by active uptake of mineral ions from the soil
what does the casparian strip do?
prevents the soil solution from continuing the diffusion through the apoplast pathway. Water is forced to pass through the endodermis symplastically after an increase in osmotic pressure by active transport of ions into the cells at the centre of the root.
types of cells that make up xylem vessels
tracheids and vessel elements
What does lignin do?
It is a hydrophobic polymer that covers the inside of the vessel tubes. It strengthens cell walls to withstand low pressures inside the vessels and prevents them from collapsing.
Adaptations of xylem for efficient water transport
short vessel elements and perforated end walls, wide and large lumens, pits in the cell wall for water entry, continuous and long columns of cells end to end for an unbroken water column.
Where does exchange of Co2 and O2 happen in plants?
through the stomata of the leaf, where water is also released in the form of vapor.
water evaporation and gas exchange in the leaf
water evaporates from the mesophyll through a concentration gradient. The air holds fewer water molecules than the air outside the leaf, allowing water to leave. The spongy mesophyll walls are moist for gas exchange. Water evaporates from them when energy is high enough to break hydrogren bonds and turn the liquid water into a gas.
controlled opening of stomata
it is controlled by guard cells, which are found in pairs on either side of the stoma. By opening and closing stoma caused by pressure changes, the amount of water lost through transpiration can be minimized.
temperature on rate of transpiration
increasing ambient temperature causes an increase in transpiration. Higher temperatures increase the rate of water vaporization.
humidity on rate of transpiration
increasing humidity causes a decrease in transpiration. Higher humidity means there is more water vapour in the air, and less vapour will be able to diffuse from the leaf.
light intensity on rate of transpiration
increasing light intensity causes an increase in transpiration. More stomata will open to facilitate photosynthetic gas exchange.
wind exposure on rate of transpiration
increasing wind causes an increase in transpiration, as wind and air circulation removes water vapour from near the leaf and reduces proximal humidity.
how to MEASURE temperature (transpiration)
using a heat lamp to vary temperature and an infrared thermometer to measure the leaf temperature. The graph will increase (linear straight slope up)
how to MEASURE humidity (transpiration)
using a transparent plastic bag to enclose a leafy shoot, and a mist sprayer to raise humidity inside the bags and desiccant bags containing silica gel to lower it. Using an electronic hygrometer measures relative humidity. The graph should be linearly decreasing (straight slope downward)
how to MEASURE wind speed (transpiration)
using an electric fan to generate air movement, varying velocity by changing the distance of the fan or the rate of rotation. An anemometer measures the speed of the air moving across the plant leaves. The graph should increase, then decrease (point parabola)
What is a potometer?
also known as a transpirometer. It is used to measure rate of water uptake of a leafy shoot. readings are taken of the movement of the air bubble along a ruler in a given time.
Pressure in xylem vessels
When atmospheric humidity or transpiration isn't occuring, xylem vessels become air filled and sap goes to roots again, pressure is positive and there is no tension. To refill xylem vessels, negative root pressure needs to be generated. To increase the pressure, active transport from adjacent endodermis cells makes the sap hypertonic and causes the water to move in through osmosis, pushing the sap upwards.
What is water potential?
the potential energy of water per unit volume, relative to pure water. It is expressed in units of pressure and used to quantify the tendency of water to move from dilute to concentrated solutions due to osmosis.
What makes a high potential energy for movement?
water with a low concentration of solute.
what makes water have low potential energy for movement?
a high concentration of solute, because the water molecules have formed hydrogen bonds with the solute, which restricts the freedom of movement of water.
What is solute potential?
Also called osmotic potential. It is the component of water potential which establishes when a solute dissolves in water. Dissolving a solute in water lowers the water potential andd makes it negative.
What is pressure potential?
The rises or falls in hydrostatic pressure that change the potential energy of water. Atmospheric pressure has a pressure potential of zero, and a living organism is affected if it rises or sinks below 0.
What happens to plan cells above atmospheric pressure?
plant cells become turgid
What happens to plant cells below atmospheric pressure?
sap in xylem vessels is pulled up to the leaves under tension
Water potential and movements in Hypotonic solutions
water moves into the cell and the number of molecules inside the cell increases. increasing pressure inside causes the membrane to exert more pressure on the cell wall, causing pressure potential to increase, solute potential to decrease and water potential to increase. The cell becomes turgid.
Water potential and movement in hypertonic solutions
water moves out from the cell and there are fewer water molecules inside the cell. The decreased pressure cauuses the cell membrane to pull away from the cell wall. Pressure potential decreases, solute potential increases, and water potential decreases. The cell is now flaccid.
What is the source in plants?
The places in the plant where sugars are produced by photosynthesis (leaves and stem) or unloaded from during germination or growth (storage tissues in seeds, tap roots or tubers at the start of growth season). Sap originates from sources and is transported by phloem to sinks.
What are sinks in plants?
the storage and growing systems of the plants where sugars are needed for cell respiration or anabolic reactions to grow or develop tissues. This is where substrates are transported to (e.g buds, developing fruits and seeds).
What is translocation?
the movement of organic molecules such as sugars and amino acids from their source through the tube system of the phloem to the sink. Sugar molecules cannot pass freely through the cell membrane into the sieve tube cells and must be actively transported in the phloem membrane proteins. Carbohydrates are produced in leaves and stems and act as sources, and amino acids are produced in the sources.
What is a companion cell
a cell in the phloem vessel that contains many mitchondria to produce ATP, which (with sucrose) passes through gaps (plasmodesmata) to sieve cells.
What is a sieve tube element?
part of the phloem vessel which acts as channels through which carbohydrates and amino acids are transported. They have reduced cytoplasm and no nucleus, membranes, or vacuoles for efficiency. However, they are alive unlike xylem. The walls are rigid for generating high pressures for hydrostatic pressure.
What are sieve plates?
plates between each sieve tube cell, formed by the holes between adjacent cells. Phloem sap can flow through them, and they load and unload sugars by active transport using ATP. THe reduced cytoplasm of sieve tube cells and the large pores allow for resistance to the flow of phloem sap to be lower
What is phloem loading?
the process whereby carbohydrates enter the sieve tube by the source through the companion cells.
process of phloem loading
sucrose is transported into phloem (actively), H+ ions transport (actively) out of the cell using ATP (apoplastic loading). High H+ concentration gradient made outside the cell, allowing H+ ions to flow back in. The energy released is used to co-transport sucrose.
concentration of solutes in phloem loading
concentration of sucrose in phliem cells is relatively high, and water is relatively low. Water moves down the concentration gradient from the xylem, through the membrane, and into the phloem cells via osmosis
hydrostatic pressure in phloem loading
water is incompressiblle and the wals of the sieve tubes are rigis, building up hydrostatic pressure at the source. Water and the solutes flow down the hydrostatic gradient to the sink where pressure is relatvely low. This is due to actie unloading of sucrose (and loss of water)
What is a flower?
the reproductive unit of an angiospermophyte
sexual reproduction in flowering plants
flowers have male and female parts which produce sex cells (gametes) required for sexual reproduction. Flowers are used for sexual reproduction, where meiosis gamete (pollen), production, and fetilization occur. A zygote is produced and retained inside the ovaries of the female parent and supplied with food as it grows and develops into an embryo inside a seed.
What are carpels?
the female parts of a flower. They have an ovary and a stigma. The two are connected by the style
Contents of the ovary (flower)
Contains one or more ovules. One cell within the ovule is called the megaspore and is diploid, which divides by meisosis to produce 4 haploid cells. Three of the cells degenerate while one divides by mitosis to produce 8 haploid nuclei. One is the female gamete or egg while two central nuclei become the pilar nuclei.
What is the stamen?
the male parts of the flower, composed of anther and filament. The anther contains 4 haploid pollen grains produced from one diploid cell. In each of these the nucleus inside divides again by mitosis to produce 3 haploid nuclei (two are male gametes). The anther contains pollen while the filament supports the anther.
What is the stigma?
the pollen landing site
What are the sepals?
they cover/protect the developing flower
What is the peduncle?
the stalk that supports the flower
What are the two nuclei in male gametes (pollen)
the tube nucleus, which grows into a tube, and the generative nucleus, which divides into two haploid sperm cells (one fertilizes the haploid egg cell, and the other fertilizes the dilpoid polar -- endosperm cells).
What is pollination?
The transfer of pollen from the anther to the stigma. Some flowering plants rely on wind or water for pollination, but most use animals (birds, bats, insects).
What is cross-pollination?
the transfer of pollen between different flowers. It is preferred as it leads to grater variation in the next generation.
Features of plants that are insect pollinated
Petals are large and brightly coloured for attraction, they are usually scented and nectar serves as food for insects. Pollen grain number is moderate. Pollen grains are stick or spikey for easy attachment to the insect's body. The anthers are located inside the flower (stiff and firmly attached) to brush against insects. The stigma is also inside the flower and is stick, allowing pollen to stick to it when insects brush it.
features of wind pollinated plants
Petals are small and dull green or brown in colour. Nectar is scentless. Pollen grains come in large number since wind pollination is more random. Pollen grains are smooth and light, and easily carried by the wind without clumping. Anthers are outside the flower and loose on long filaments to release pollen easily. Stigma are also outside the flower. They are feathery and form a network to catch drifting pollen.
What is mutualism?
a close association between two organisms where both organisms benefit from the relationship. The animal is rewarded with food in the form of nectar, and the plant is successfully pollinated.
What is self-pollination?
when pollen from the same plant is transferred to the stigma of that plant. Many plants are hermaphrodites, and produce both pollen and ovules with female gametes.
What is protandry vs protogyny
In protandry, anthers mature first, and in protogny, stigmas mature first. separation of anthers and stigmas are in sepperate female and male flowers on the same plan. Dioecious plants are plants where the female and male flowers are on different plants.
What is self-incompatibility?
If a hermaphrodite plant receives pollen from its own stamins, self-incompatibility prevents the pollen from germinating or growing. This prevents inbreeding, and plants with the same self-incompatibility alleles cannot successfully fertilize each other.
How is fruit developed?
the seed contains the developing embryo and the embryo within the seeds is surrounded by the fruit flesh which provides nutrition to the embryo. The ovule develops into the seed and the ovary develops into the fruit. The vrious parts of the female carpel and male stamen develop into the fruit which surrounds and protects the embryo.
Embryo (parts of seed)
Embryo has root (radicle) and shoot (plumule). The plumule is the rudimentary shoot of a plant, and the radicle is the embryonic root.
Epicotyl (parts of a seed)
Epicotyl is the part of the young stem above the point of attachment of the cotyledons, and the hypocotyl is below it.
Cotyledon (parts of a seed)
The cotyledon are the first leaves of a young plant and provides energy storage material for the seed.
testa (parts of a seed)
the seed coat which is water impermeable in most seeds
micropyle (parts of a seed)
small opening to allow for absorption of water, a tiny spot close to scar
What are ideal conditions for germination?
all seeds need water (taken in through the micropyle and used to activate the seed) oxygen for respiration, ideal temperatures and pH for enzyme activity. Light requirements differ between species.
fire (germination conditions)
some seeds will only sprout after exposure to intense heat (e.g after bushfires remove established flora)
freezing (germination conditions)
some seeds will only sprout after periods of intense cold (e.g in spring, following the winter snows)
digestion (germination conditions)
some seeds require prior animal digestion to erode the seed coat before the seed will sprout
washing (germination condtions)
some seeds may be covered with inhibitors and will only sprout after being washed to remove the inhibitors.
scarification (germination conditions)
seeds are more likely to germinate if the seed coat is weakend from physical damage.
steps of germination
1. the radicle emerges first and anchors the seedling in the soil water and absorbs water and mineral ions.
2. The young embryo stem emerges as the testa is split away from the cotyledons. The hooked shoot protects the young leaves from damage by soil particles.
3. The stem grows upwards, retaining its hooked shape.
4. Foliage leaves show. The shoot (plumule) emerges above the ground and starts to straighten out to lift foliage leaves above the soil.
Dry mass levels during germination
Dry mass falls as part of food store is consumed by respiration, mass falls more quickly as growth of the seedling accelerates. Then, mass begins to increase as th first foliage leaves start to build up food compounds by photosynthesis.
Steps of germination of starchy seeds
1. water is absorbed through the micropyle and activates cells in a process called imbibition.
2. Synthesis of gibberelins (plant growth hormones)
3. Gibberelins cause synthesis of amylase (enzyme)
4. Amylase hydrolyses stores starch to maltose
5. Maltose absorbed by plumule and radicle
6. Further hydrolysis breaks maltose into glucose, which is used for respiration in the growing tissues
What is gibberellic acid?
it is a plant growth substance produced by the cells in the embryo. It passes to the food stored in the cotyledons, where protein reserves are converted to hydrolytic enzymes which mobilize the stored food reserves.
Hormone production in seed germination steeps
1. water absorption (eventually causes the testa to split)
2. the embryo produces GA
3. GA passes to food storage cells
4. Hydrolytic enzymes are produced that covert stored startch to glucose and proteins to amino acids
5. Glucose and amino acids are translocated to growing points of stem and root.