Botany Flashcards
What are the two methods of pollination?
Flowering plants have evolved two pollination methods: 1) pollination without the involvement of organisms (abiotic), and 2) pollination mediated by animals (biotic). About 80% of all plant pollination is by animals. The remaining 20% of abiotically pollinated species is 98% by wind and 2% by water.
What is apical dominance?
The phenomenon whereby the main, central stem of the plant is dominant over (i.e., grows more strongly than) other side stems; on a branch the main stem of the branch is further dominant over its own side twigs.
What occurs to prevent seed germination?
Seeds might have a hard or thick seed coat (physical dormancy). This can be broken by soaking or scarifying (scratching the surface) the seed.
Other seeds have internal chemical or metabolic conditions that prevent germination (chemical dormancy). Factors affecting seed dormancy include the presence of certain plant hormones–notably, abscisic acid, which inhibits germination, and gibberellin, which ends seed dormancy.
What is endosperm?
Endosperm, tissue that surrounds and nourishes the embryo in the seeds of angiosperms (flowering plants).
What is nitrogen fixing?
Nitrogen-fixing plants form a mutually beneficial symbiotic relationship with soil bacteria. Inside these root nodules, the bacteria draw nitrogen gas from the air, turning it into fixed nitrogen that is able to be absorbed and used by the plant host.
What are three methods of nitrogen fixation?
Free-living bacteria fixation
Associated bacteria fixation
Symbiotic bacteria fixation (including legume nodule formation)
Name two biennial plants
Foxglove
Parsley
Name two annual plants
Calendula
Sunflower
Name two perennial plants
Hawthorn
Guelderrose
What is High Performance Liquid Chromatography?
High Performance Liquid Chromatography (HPLC) is a form of column chromatography that pumps a sample mixture or analyte in a solvent (known as the mobile phase) at high pressure through a column with chromatographic packing material (stationary phase).
What is translocation?
Photosynthesis produces glucose in the green parts of plants, which are often leaves. This is then converted into sucrose. The sucrose is transported around the plant in phloem vessels. It needs to be able to reach all cells in the plant so that the sucrose can be converted back into glucose for respiration. The movement of sucrose and other substances like amino acids around a plant is called translocation. In general, this happens between where these substances are made (the sources) and where they are used or stored (the sinks):
from sources in the root to sinks in the leaves in early spring time
from sources in the leaves to sinks in the root in the summer
Compare and contrast xylem and phloem
Xylem: Transpiration, Moves water and minerals from roots to leaves, Columns of hollow, dead reinforced cells
Phloem: Translocation, Moves food substances from leaves to rest of plant and from stores such as in the roots, Columns of living cells
Why is hydrogen bonding important for transpiration?
Water molecules inside the xylem cells are strongly attracted to each other. There is strong cohesion between the molecules because of hydrogen bonding. A continuous column of water is therefore pulled up the stem in the transpiration stream by evaporation from the leaves.
What is the purpose of transpiration?
As water travels through the xylem in the stem and leaf, it is being replaced by water taken up by the roots.
Transpiration is an unavoidable consequence of photosynthesis – only five per cent of the water taken up by the plant is used for photosynthesis – but does have its purposes:
provides the water for photosynthesis
transports mineral ions
cools the leaf as water evaporates
provides water that keeps the cells turgid, which supports herbaceous (non-woody) plants
How does water and minerals enter the plant?
Root hairs are single-celled extensions of epidermal cells in the root. They grow between soil particles and absorb water and minerals from the soil.
Water enters the root hair cells by osmosis. This happens because soil water has a higher water potential than the cytoplasm of the root hair cell. Minerals enter by active transport.
What are the forms of biologically available nitrogen?
Ammonium ions –> Nitrites –> Nitrates
What is denritification?
Denitrification is the microbial process of reducing nitrate and nitrite to gaseous forms of nitrogen, principally nitrous oxide (N2O) and nitrogen (N2). A large range of microorganims can denitrify. Denitrification is a response to changes in the oxygen (O2) concentration of their immediate environment (ie. waterlogged soil)
What is ammonification?
The process of decomposing bacteria which turns nitrogen in organic material into ammonium ions.
What is the nitrogen cycle?
Ammonium ions –> (bacteria) –> Nitrites –> (bacteria) –> Nitrates –> Plants –> Animals OR Decomposers –> Decomposers –> Ammonium ions
What is pharmacognosy?
the study of drugs of natural origin.
What is thin layer chromatography (TLC)?
Thin-layer chromatography is a chromatography technique used to separate non-volatile mixtures. Thin-layer chromatography is performed on a sheet of an inert substrate such as glass, plastic, or aluminium foil, which is coated with a thin layer of adsorbent material, usually silica gel, aluminium oxide, or cellulose.
What is the life cycle of an angiosperm?
Dormant Seed Dispersal Breaking Dormancy Germination Growth and development Flowering Pollination Fertilization and Seed Development
What is a monocotyledon?
Seeds contain one embryonic leaf. Flowers and leaves organized in 3s. Leaves have parallel veins.
In the monocotyledon, the scutellum absorbs digested nutrients from the endosperm (a starch store), during germination and early growth.
What is a dicotyledon?
Has two embryonic leaves. Leaves have branching veins. In the dicotyledon, the cotyledons form the initial food store but go on to emerge from the soil, and develop ‘seed leaves’ which look quite different from the leaves of the mature plant. They then photosynthesise, making food for the growing seedling.
Why is seed dispersal important?
To ensure that at least some of the offspring of a plant ends up in conditions suitable for their growth. For perennial plants it is important that seedlings aren’t competing with their parent for water, nutrients and light.
How are seeds dispersed?
Most seeds are dispersed by wind or birds and animals, a few e.g. the coconut, by water and some like Sarothamnus (broom) have a mechanism which flings the seeds from a pod which splits explosively when it dries.
How is the development of fruit advantageous?
The structure which contains the seeds is a fruit, derived from the ovary of the flower. The fruit may be attractive and sweet tasting so that it is eaten; the seeds are softened by digestive juices but survive to be deposited with faeces rich in nitrate and phosphate. Some, e.g. Rubus species, contain powerful laxatives to aid the process. Other fruits are inedible, such as the winged seed-bearing fruits of Fraxinus (Ash) and Ulmus, (Elm), and the parachute of Taraxacum (Dandelion), all of which are wind-dispersed, and the barbed fruits of Geranium species and Arctium which rely on clinging to animals and being rubbed off later.
What is seed dormancy?
Dormancy is a period which prevents the seed from germinating in unsuitable conditions and allows time for dispersal, so maximizing its chance of surviving and ultimately reproducing. During this time metabolism is minimal and hard protective outer layers protect the embryo from infection and climatic extremes.
What are some ways of breaking dormancy?
Some seeds need to pass through the digestive tract of an animal or bird, others need light or the absence of light, some must be scarified – physically abraded by soil and rocks- or the trigger may be increasing temperature or degradation of inhibitory chemicals in or on the seed.
What are some examples of breaking dormancy?
Apium graveolens (celery) needs cool soil to germinate.
Lactuca spp. (lettuce) need a spell of cold, called stratification.
Many Gramineae (Poaceae) species (grasses) need a dry spell first.
Iris spp. Have chemicals in the endosperm which must break down to allow germination to begin.
Pinus sylvestris cones stay closed until there is a forest fire and only then release the seeds ready for germination. (Note that Pinus spp. are in fact Gymnosperms, ‘naked seeded’ plants, not Angiosperms, which produce enclosed seeds).
What is germination?
When the seed is in conditions suitable for growth and (where necessary), dormancy has been broken, water will be taken up by imbibition and this will activate enzymes that break down the insoluble food store into soluble sugars which are then available to the developing embryo
What is the radicle?
Embryonic root
What is the plumule?
Initial shoot growth
How is starch broken down into glucose?
Starch (enzyme: Amylase) –> Maltose (enzyme: Maltase) –> Glucose
What are the initial stages of seed growth?
The embryonic root (radicle) grows first, so that water can then be taken up from the soil and shoot growth (plumule) follows, producing leaves which can photosynthesise. Sugars can then be made to sustain the plant after the seed nutrients have been used up.
These are active processes which require energy from respiration which in turn needs oxygen, so germinating seeds must not be waterlogged.
What is meristem?
The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants.
What are primary meristems?
All plants have primary meristems just behind the apices of root and shoot and these produce their increase in height.
What are secondary meristems?
Some plants have secondary meristems which cause an increase in girth; these are mainly found in perennial dicotyledons.
Summarize the cell cycle
G1, S and G2 = interphase
Go is the phase when a cell leaves the cycle, either temporarily or permanently, e.g. because it is damaged, or has become specialized for a particular function.
There are 3 very important checkpoints:
1. During growth phase 1 (G1) to check that the cell has all the organelles needed and is at the right size for division
- At the end of the second growth phase (G2).
- After DNA replication to check that the chromosomes have been accurately copied, and during division in metaphase to ensure accurate alignment of chromosomes on the equator of the spindle so that the genetic material is evenly distributed in anaphase. Mitosis actually occupies a very small portion of the cell cycle.
The rest comprises the essential events of interphase which prepare and equip the cell for division.
What is a tonoplast?
Membrane around vacuole
What is a vacuole?
A vacuole is a membrane-bound cell organelle. In plant cells, vacuoles help maintain water balance. Sometimes a single vacuole can take up most of the interior space of the plant cell.
What is cell sap?
chemical palette of the vacuole solution
What is a plasmodema (plasmodesmata pl.)?
Plasmodesmata are minuscule plasma corridors between plant cells which are of paramount importance for transport, communication and signalling between cells. These nano-channels are responsible for the integrated action of cells within tissues and for the subdivision of the plant body into working symplast units.
What is the middle lamella?
The middle lamella serves as a cementing layer between the primary walls of adjacent cells.
What are chloroplasts?
Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide gas to produce food for the plant.
Chloroplasts capture light energy from the sun to produce the free energy stored in ATP and NADPH through a process called photosynthesis.
Chloroplasts are one of the many unique organelles in the plant body, and are generally considered to have originated as endosymbiotic cyanobacteria.
What is the Golgi apparatus?
The Golgi apparatus is responsible for transporting, modifying, and packaging proteins and lipids into vesicles for delivery to targeted destinations.
What are vescicles?
created by Golgi apparatus to package and transport proteins and lipids to target destinations
New cells produced by mitosis elongate under the influence of the hormone…
auxin
How do hormones travel in the plant?
diffuse from cell to cell
What is phototropism?
a growth response. When a plant is exposed to light from one side, auxin gathers in the shaded side of the shoot and causes elongation of the cells on that side, which makes it bend towards the light.
What causes apical dominance?
Auxin is continually made in the shoot tip and diffuses downwards, accumulating around the nodes beside lateral buds. Its presence here inhibits lateral shoot growth, so if you want a bushy plant, you need to remove the terminal region and so remove the area which produces auxin.
What are the roles of giberellin?
- promotes lateral shoot growth in the absence of auxin
- gibberellins produced by the embryo also play a part in the germination of some seeds by stimulating the production of enzymes which mobilise the food reserves.
What is ethene?
Ethene is produced by ageing or mature tissues as a gas which diffuses through the air spaces between cells. It promotes the ripening of fruit.
Ethene is also involved in leaf drop – young leaves produce auxin but not ethene. As they age the amount of auxin produced reduces and ethene is produced.
What is the abscission layer?
The abscission layer, a barrier of thin-walled parenchyma cells, develops across the stem (or petiole) at the base of a leaf, flower, or fruit as it approaches the time of falling from a plant.
What is abscisic acid?
abscisic acid is produced when a plant is under stress, for example lack of water or extreme cold. It stimulates the stomata to close, so reducing water loss by evaporation from the leaves.
What are some commercial uses of auxins?
synthetic auxins used as herbicides
indole acetic acid (IAA), naturally-occurring auxin, used as rooting hormone
coordinate fruit production
stimulate fruiting in sterile species such as seedless cucumbers
What are some commercial uses for gibberellins (gibberellic acid)?
Gibberellins (gibberellic acid) - Gibberellins (GAs) are a group of plant hormones that stimulate shoot elongation, seed germination, and fruit and flower maturation. GAs are synthesized in the root and stem apical meristems, young leaves, and seed embryos.
In urban areas, GA antagonists are sometimes applied to trees under power lines to control growth and reduce the frequency of pruning.
GAs break dormancy (a state of inhibited growth and development) in the seeds of plants that require exposure to cold or light to germinate. Abscisic acid is a strong antagonist of GA action. Other effects of GAs include gender expression, seedless fruit development, and the delay of senescence in leaves and fruit. Seedless grapes are obtained through standard breeding methods; they contain inconspicuous seeds that fail to develop. Because GAs are produced by the seeds and because fruit development and stem elongation are under GA control, these varieties of grapes would normally produce small fruit in compact clusters. Maturing grapes are routinely treated with GA to promote larger fruit size, as well as looser bunches (longer stems), which reduces the incidence of mildew infection.
What are xylem vessels?
Xylem vessels, which carry water from the roots to the leaves, consist of columns of cells which lose their end walls and become unbroken tubes. The mature cells are dead because they lack any contents to carry out living processes, and their walls are thickened and strengthened with a waterproof substance, lignin, in various patterns.
What is lignin?
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily.
How does transpiration take place?
As water evaporates, it ‘pulls’ a chain of water molecules up. They form a chain due to the cohesive forces between them and to the adhesive forces between the water molecules and the sides of the xylem vessels. Another contributory factor is root pressure, a consequence of continual water uptake by root hair cells.
This depends on diffusion which is an important concept in plant and animal physiology.
What is the Casparian strip?
The Casparian strip is a specialized layer of cells just outside the vascular tissue of the root. It has suberin in its walls, which forces the water to take the symplast pathway and allows selective uptake of mineral ions.
What are the three pathways of water intake?
Symplast is via the cytoplasm
Apoplast is seeping between cell walls
Vacuolar is between vacuoles
What are the layers of a leaf?
A Waxy Cuticle B Upper epidermis C Palisade cells D Spongy cells E Stomatal pore
What is the equation of photosynthesis (simplified)?
water + carbon dioxide –> glucose + oxygen
What are the two stages of photosynthesis?
The light dependent stage is where light energy is harvested by pigment molecules e.g. chlorophyll, in the thylakoid membranes of chloroplasts, and the products are ATP and the reduced hydrogen acceptor NADPH .
The light independent stage or Calvin cycle uses the ATP and NADPH in combination with CO2 to make glucose.
What are thylakoids?
a series of membranes in chloroplasts where the light-dependent reactions take place
How is the rate of photosynthesis effected?
The rate at which photosynthesis can proceed will depend on the factor which is least favourable. This could be CO2 availability, light intensity or temperature.
The Calvin cycle relies on enzyme activity and since enzymes are very temperature-dependent, plants will often have quite a narrow range at which they function best and this will depend on their area of origin.
Describe phloem tissue
Transport of food is in phloem tissue which like xylem consists of tubes made from chains of cells, but unlike xylem it is still living. The end walls of the sieve tube elements do not break down completely and there are some contents in the cells. However, this is not enough to maintain the cells and actively move sugars, so each cell has a companion cell which can carry out the necessary metabolic processes.
How is glucose used within the plant?
Glucose can then be used as an energy source or converted into other nutrients that the plant needs. For example:
It can be built up into the polysaccharide cellulose for cell walls
it may react with nitrates to make amino acids, the building blocks of proteins e.g to make enzymes.
It can enter a biochemical pathway that produces lipids (fats and oils) e.g. for seeds.
Why does the plant make glucose, transport it as sucrose and store it as starch?
Starch is water insoluble so does not affect the way water moves in and out of the cell.
Sucrose is a disaccharide so it is easier to transport higher concentrations of energy in these larger molecules.
What are rhizomes?
Rhizomes are an underground horizontal stem which store food and have nodes with buds and scale or foliage leaves. Zingiber, Convallaria and Iris all have rhizomes.
What are tubers?
Tubers are a swollen underground stem or root which stores food and has buds e.g the ‘ eyes’ of a potato.
What are bulbs?
Bulbs are a compressed shoot with fleshy storage leaves e.g. Allium spp
What are corms?
Corms do not have the fleshy leaves like a bulb but are a food store in a stem e.g. Crocus spp.
What are suckers?
Suckers are basal shoots which grow from a bud on a root. These are often close to the parent plant but do arise a distance away e.g. Ulmus spp.
What are stolons?
Stolons (runners) grow from the base of the plant e.g. Fragaria spp.
