Botany Flashcards
Describe the life cycle of an angiosperm
- Dormant seed
- Dispersal
- Breaking dormancy
- Germination
- Growth and development
- Flowering
- Pollination
- Fertilisation and seed formation
Angiosperm
Plants that produce flowers and bear seeds in their fruits. The seeds develop in the ovaries of flowers and are surrounded by a protective fruit.
Gymnosperm
Plants that have seeds unprotected by an ovary or fruit eg. conifers.
Monocotyledons (monocots)
Flowering plants (angiosperm).
Contains one seed leaf (cotyledon) eg corn.
Dicotyledons (dicots).
Flowering plants (angiosperm).
Contains 2 seed leafs (cotyledons). eg. Broad bean.
What is a seed?
It consists of an embryo plant and a food store surrounded by a protective coat.
Name for seed coat
Testa or also known as a pericarp
Endosperm
This is the food store inside a monocot seed
Endosperm in a dicot
This is labelled as cotyledon
Scutellum
This is only ever labelled in a monocot seed, and is sometimes referred to as the cotyledon
A baby shoot in a seed
Plumule, sometimes labelled as epicotyl instead
A baby root in a seed
Radicle
Coleoptile
This is found only in monocots. It is a cap/sheath which protects the plumule, as it comes up through the soil.
Coleorhiza
Only exists within monocots. It is a cap which protects the radicle as it moves through the soil - similar to coleoptile.
Aleurone layer
This is the protein of the seed.
Monocotyledon germination process
The scutellum absorbs digested nutrients from the endosperm (a starch store), during germination and early growth.
Dicotyledon germination process.
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.
4 herbs used medicinally for their seeds
Avena sativa
Aesculus hippocastanum
Plantago spp.
Foeniculum vulgare.
Why is seed dispersal important?
It’s vital to ensure that at least some of the offspring of a plant end up in conditions suitable for their growth.
Perennial plants - important seedlings aren’t competing with their parent for water, nutrients and light.
Meristematic tissue
This is found within the radical and plumule of the dicot seed
Hilum
This is where it joins to the wall of the seed, the belly button
Micropyle
This is a tiny hole where the pollen shoot goes down into the seed
Seed dispersal mechanism examples
Windblown fruits
Adherent fruits
Fleshy fruits
Water dispersed
Self dispersal
Windblown fruits definition and examples
Dry, light, small and usually have wind-like or parachute like structures.
Eg. Acer saccharum (Sugar maple)
Asciepias syriaca (common milkweed)
Adherent fruits definition and examples
These have hooks or stiff hairs, to stick to the fur of animals and be taken to a different area and be rubbed off later.
Eg. Arctium spp. Geranium spp.
Fleshy fruits definition and examples
Juicy, fragrant, sweet or brightly coloured fruits. Attractive so that it is eaten, then softened by digestive juices and survive to be deposited with faeces rich in nitrate and phosphate.
Eg. Rubus sp.
Juniperus chinensis
Water dispersal definition and examples
These contain a waterproof layer of fibrous husks, and are carried via floating on water for long distances (streams etc).
Eg. Coconut
Self dispersal definition and examples
These are fruit walls that split open with explosive force when they are ripe. Examples include geranium spp. and urtica dioica.
Dormancy
Is a period which prevents the seed from germinating in unsuitable conditions and allows time for dispersal, maximising it’s chance of surviving and reproducing.
During this time metabolism is minimal and hard protective outer layers protect the embryo from infection and climate extremes.
How is dormancy achieved?
- Seed coat impermeability (this can be broken by a number of events, eg. fire, scarification - this happens in nature by seeds tumbling against stones, dry heat - fire, light, various chemicals)
- Internal physiological mechanisms involving enzyme inhibition (eg by abscisic acid, temperature change such as stratification, and changes in day length).
Examples of breaking dormancy
- Apium graveolens (celery) needs cool soil to germinate
- Lactuca spp (lettuce) needs a spell of cold, called stratification
- Many Poaceae species 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, an only then release the seeds ready for germination.
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.
Imbibition
This is the uptake of water by the seed
Describe the germination cycle
Water is absorbed into the seed through the testa via Imbibition.
This water activates a hormone (Gibberellin),
The hormone then triggers amino acid release & enzyme synthesis from the aleurone layer.
The enzymes catalyse the hydrolysis of food stores eg. the enzyme amylase which converts starch to maltose, an the enzyme maltase converts maltose to glucose.
The glucose is then used by the embryo for respiration and the radicle grows first so that water can be taken up from the soil.
Meristems
This is the area of a plant which actively grows. This is where cell division by mitosis takes place. There are primary and secondary meristems.
Primary meristems
All plants have these just behind the apices of root and shoot. These produce an increase in height.
Secondary meristems
Only some plants have these. They cause an increase in girth, and are mainly found in perennial dicotyledons.
Mitosis
When a cell divides by mitosis it produces two cells which are identical to each other and to the parent cell. Before this can happen, all the organelles and the genetic information in the nucleus must be replicated.
The cell cycle
G1, S and G2 = Interphase
G1 = Cellular contents, excluding chromosomes are duplicated
S = Each of the 46 chromosomes is duplicated by the cell
G2 = The cell double checks the duplicated chromosomes for error, making any needed repairs.
Prophase
Metaphase
Anaphase
Telophase
Go = the phase when a cell leaves the cycle, either temporarily or permanently due to being damaged or it has been specialised for a [articular function
Where are the 3 important checkpoints during the cell cycle?
- During the growth phase (G1)
- 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.
Mitochondrion
The synthesis of ATP inside a plant cell
Envelope
Double layer - found on a chloroplast and a nucleus
Grana
Found within the chloroplast. They are thylakoid membranes which are very important structures. They are small, thin and can be stacked up into structures. They are connected to eachother by thin pieces of thylakoid membrane called lamellae.
Grana contain chlorophyll.
Rough ER
Function is protein synthesis
Nucleus
Contains nucelar pore, nucleolus, chromatin and nuclear envelope
Nuclear envelope.
Separates the contents of the nucleus from the cytoplasm and provides the structural framework of the nucleus.
Nucleolus
Found in the nucleus. Produces and assembles the subunits which form the ribosome
Nuclear pore
Found in the nucleus. Facilitates and regulates the transport of molecules across the barrier provided by the nuclear envelope
Chromatin
Found in the nucleus. To compress and package long DNA molecules into compact dense structures
Ribosomes
Performs protein synthesis from translating the information contained in mRNA molecules