D3.1 Reproduction (plants) Flashcards
Why are there different strategies for reproducing in plants?
Because plants cannot move.
What is sexual reproduction known as in plants?
Flowering plants or angiosperms
What is hermaphrodites?
Many plants are hermaphrodites with flowers that contain both male and female parts.
How do plants sexually reproduce with two parents?
However, in some species, this is not the case and there are male and female flowers on the same plant (e.g. hazel) or on different plants, e.g. kiwi and papaya.
What do ovule contain? And what happens when that is fertilized?
An ovule contains an ovum as well as a store of nutrients. Once the ovum is fertilised it becomes a seed.
What is the male reproductive cells in plants?
The male reproductive cells are pollen which travel to the female reproductive part in the same plant, or in another plant, carried by wind or insects.
What is pollination
Pollination is the transfer of pollen from the anthers of one flower to the stigma of another. Multiple pollen grains land on the stigma.
What happens when pollen lands on the stigma?
The pollen grain then germinates and the pollen nuclei travel through a pollen tube down the style, the ovary , the ovule and finally the ovum where fertilization occurs, producing an embryo.
How does the pollen enter the ovule?
They enter the ovule through a tiny opening called the micropyle.
What is double fertilization?
There are two male nuclei, one will fuse with the ovum nucleus in the embryo sac, forming a diploid zygote. The other nucleus fuses with another nucleus of the ovum, triggering the formation of the food store for the developing embryo. This is called ‘double fertilization’ and is unique to flowering plants.
Where are the different parts of the flower found?
The different parts of the flower are found in rings or whorls attached to the swollen tip of the stalk which is called the receptacle.Not all the parts of a flower are always present, e.g. tulips lack sepals. If all the parts are present the flower is called a complete flower, otherwise it is an incomplete flower.
Do all flower have all parts? What are they called if they do?
Not all the parts of a flower are always present, e.g. tulips lack sepals. If all the parts are present the flower is called a complete flower, otherwise it is an incomplete flower.
What is cross pollination?
Cross pollination is favourable to flowering plants. In this method, pollen from one flower is transferred to a different plant of the same species.
Are insect pollination plants only for insects?
No, also hummingbirds and bats.
How do plants reproduce successfully?
For plants to reproduce successfully a lot of pollen needs to be transferred from the anthers to the stigma of a flower of the same species. Plants use a variety of strategies for this to happen and increase their chances of successful fertilization.
How is cross-pollination achieved?
Cross-pollination is achieved by:
* the stamen and stigma maturing at different times
* the stigma and anthers at different heights in the same flower
* separate male and female flowers e.g. kiwi and papaya
* Self-incompatibility mechanisms which prevent hermaphrodite flowers from producing zygotes if self-pollinated
What do self-pollination and cross-pollination result in?
Self-pollination results in inbreeding.
Cross-pollination results in outbreeding
Why is cross-pollination more advantageous?
Advantage: variation and some genomes more successful than others - evolutionary advantage if there is selection pressure due to e.g. changes in the environment.
What are the disadvantages of cross-pollination?
Disadvantage: pollen needs to land on the stigma of flowers of the same species which depends on an element of chance, especially in wind-pollinated flowers AND reduces variation, increasing the chance that two undesirable recessive alleles come together.
What occurs when fertilization is successful?
When fertilization is successful a number of changes occur in the flower. The external whorls (sepals, petals and stamens) drop off. Inside the ovule, the zygote divides by mitosis to form an embryo and the triploid cell develops into the endosperm.
What happen to the ovule after fertilisation?
The wall of the ovule hardens and becomes the seed coat or testa which protects the developing embryo and the endosperm.
What happens after fertilisation to the ovary?
The ovary swells and forms the fruit (pericarp). The water content of the seed decreases and the seed enters a dormancy period.
What is seed dispersal?
the carrying of seeds away from the parent plant
What is germination? And what is cell called until germination?
Germination of the seed is the development of the seed from the moment it starts to take up water and results in the emergence of the radicle. It can only happen when the conditions for germination are favourable. Until that moment the seed remains in DORMANCY.
What are the conditions required for germination?
- Imbibe water and swell up, causing the seed coat to rupture
- Respiration, which was suspended or much reduced during dormancy, resumes and the rate of respiration increases
- Food reserves from the endosperm must become available; the carbohydrates, proteins and lipids need to be hydrolysed and translocated (studies in cereals show that following the imbibition of water, gibberellins start to be produced by the embryo; these hormones cause the release of enzymes that break down the stored food reserves into simple sugars, amino acids and fatty acids, allowing the food to be absorbed by the cotyledons and transported to the growing embryo).
- Development of the embryo into a seedling with the emergence of the primary root or radicle (marking the end of germination) followed by emergence of the plumule - a seedling has formed.
- Germination often happens in the soil and light is only required for further growth of the plumule once the shoot tip is exposed to light.
What are flowers?
Flowers are the reproductive structures in flowering plants or angiosperms.
What is a typical flower structure?
A typical flower is a complex structure composed of four layers.
What are the four features present in flowers?
The layer that you are probably most familiar with is the petals. In addition, there are the leaf-like sepals, the stamens or the male reproductive structures, and the pistils (carpels) or the female reproductive structures.
What is a perfect flower known as?
A perfect flower is one that has the male and the female parts. This means the flowers could have both stamens and pistils – these flowers are bisexual (hermaphroditic) flowers.
What is imperfect flower known as?
An imperfect flower has either the male or female parts. These flowers may have either the stamens or the pistils, these flowers are unisexual flowers.
What is does the stamen consist of?
Each stamen consists of two parts: a tube-like filament and a sac-like anther.
What is present in the anthers?
Present within the anther are the pollen grains.
What do pollen grains consists of? And what occurs once matured?
The pollen grains, when mature, are released from the anther. Each pollen grain consists of a generative cell and a larger tube cell. Two layers, an outer tough exine and an inner intine made of cellulose, surround the tube cell.
What is a pistil or carpel?
The pistil is located in the centre of the flower and consists of three regions: the swollen base or the ovary, the stalk or style and the stigma.
What do the ovaries contain?
The ovary contains the ovules.
What do the ovules contain?
Inside each ovule is the embryo-sac with seven cells and eight haploid nuclei.
What does sexual reproduction in plants involve?
Sexual reproduction in plants involves the fusion of the male gametes (sperm cells) within the pollen with the female gametes (the egg) to form a diploid zygote.
What needs to take place before fertilisation?
Before fertilisation can take place pollination needs to have occurred. This is the process by which the pollen grains are transferred from stamen –> carpel. (specifically anther –> stigma)
How does pollination occur?
Pollination takes place with the help of modulators e.g. insects & other animals, wind & even water.
What happens when multiple pollen grains land on the stigma (pollination)?
Once a pollen grain reaches the stigma, it begins to germinate. The tube cell elongates forming the pollen tube. The pollen tube grows down the length of the style into the ovary in response to the chemicals secreted by the synergids. The generative cells divide mitotically to form the sperm cells. The sperm cells move through the tiny opening or micropyle into the ovule.
What happens during fertilisation?
One of the sperm nuclei fuses with the egg to form the diploid zygote. This, in turn, develops into the embryo. The second sperm nucleus fuses with the central cell. Remember that the central cell consists of two haploid polar nuclei. Hence, this process = triple fusion & results in a triploid cell (3n). This triploid cell gives rise to the endosperm, which surrounds and nourishes the developing embryo.
What is the name for the process of fertilisation & triple fusion?
The entire process of fertilisation and triple fusion is known as double fertilisation and is seen only in flowering plants.
What is necessary for plants to reproduce successfully?
For plants to reproduce successfully, enough pollen must land on the stigma of flowers - in other words, the rate of pollination must be high.
How is the stamen adapted in flowers have to ensure that pollination happens?
Stamens = male reproductive parts. They consist of a filament & an anther.
a) Filament = stalk-like structure that attaches anther to flower stem.
b) Anther = sac-like structure that encloses pollen grains. Pollen grains vary in shape, size & texture from one plant species to another.
How are the pistils/carpels adapted in flowers have to ensure that pollination happens?
The pistils/carpels = female reproductive structures.
a) Stigma = sticky, which pollen grains land & germinate.
b) Style = slender tube that connects stigma to ovary.
c) Ovary = swollen base of pistil & contains one or more ovules.
How are the petals adapted in flowers have to ensure that pollination happens?
The petals = large & brightly coloured.
- Often have nectar-producing glands at their base or are fragrant.
- Petals can be fused together to form a tube or can be separate.
- Some flowers, petals modified, forming landing platforms for insects.
- Petals are collectively known as corolla.
How is the calyx adapted in flowers have to ensure that pollination happens?
The calyx = ring of green leaf-like sepals that forms the outermost layer of the flower. Sepals = protective in nature. Sometimes, sepals are brightly coloured too.
What is the receptacle?
The receptacle = thickened part of the stem at the base of the flower
How are flower pollinated, when its an insect pollinating plants?
In insect pollination, the pollen grains are carried from one flower to another by the insects.
What are the adaptation of insect pollinating plants?
- Some flowers produce nectar, a popular insect food, to lure insects. As insect drinks the nectar, anther brushes against its legs, transferring pollen. When insect visits another flower, some pollen gets transferred to stigma, resulting in pollination.
- Some flowers (e.g. Magnolia, lilies (Lilium)) have developed strong scents to attract insects.
- Others are white or brightly coloured to attract insects.
- Pollen produced by insect-pollinated flowers = heavy & sticky to ensure that pollen gets stuck to body of insect.
How have plants adapted to ensure pollen isn’t wasted?
To ensure that pollen isn’t wasted on a plant of another species, flowers have evolved in ways to encourage visits by a few specific pollinators. E.g. colour & scent of pea flowers attract bees. Thus, flowers & insects have evolved leading to symbiotic relationships.
Label the diagram.
- Pistil
- Stigma
- Style
- Ovary
- Petal
- Receptacle
- Sepal
- Anther
- Filament
- Ovule
- Stamen
What are the two types of pollination?
- Cross-pollination
- Self-pollination
What is cross-pollination?
Cross-pollination = transfer of pollen grains from one flower on one plant to stigma of another flower on another plant
What is self-pollination?
Self-pollination = transfer of pollen grains to stigma of same flower or to stigma of another flower on same plant
How does pollination occur in cross-pollination?
The pollen grains are transferred by animals including insects, birds and bats, & by wind.
What plants tend to use wind to pollinate?
Many grasses and cereal crops are pollinated by wind.
What are the adaptation to plant a plant that use wind to pollinate?
- Flowers = small, unscented & don’t have nectar (meaning no nectar glands)
- Pollen grains = lighter so that they can be easily carried by wind & produced in larger number
- Stigma = feathery to helps ‘catch’ pollen
- Anther exposed to wind & dangle loosely from filament so that pollen is easily carried away
Why is cross-pollination an evolutionary advantage?
It is evident that cross-pollination brings in genetic diversity as male & female gametes are from two different plants. Which means when environment changes, plants with favourable variations survive & reproduce, thereby ensuring survival of species.
What are some adaptations in flowering plants that facilitate cross-pollination and prevent self-pollination?
- Some plants e.g. date palm (Phoenix dactylifera) & papaya (Carica papaya), male & female flowers are located on different plants, mandating cross-pollination.
- Plants where male & female flowers are located on same plant, maturation time of male & female flowers differs. E.g. male flowers mature before female flowers & release their pollen e.g. avocado.
- Plants with hermaphroditic flowers, time at which anthers & pistils mature varies. Pistils may mature faster than stamens e.g. arum lilies (Zantedeschia aethiopica) & vice versa. E.g. ivy (genus Hedera), carrot (Daucus carota) & Salvia anther mature & release pollen; however, stigma is still immature & non-receptive to pollen grains.
- Anatomical structure of bisexual flowers also facilitates cross-pollination. E.g. primrose (Primula vulgaris) produces two forms of flowers
What is a disadvantage of self-pollination?
Self-pollination = form of inbreeding or mating among close relatives. Genetic makeup of offspring = similar to parents, reducing genetic diversity. In a changing environment, lack of genetic diversity could be disastrous. Studies have shown that, in species where both self- & cross-pollination work, seeds produced by cross-pollination are of better quality & greater vigour.
What is self-incompatibility?
Self-incompatibility = inability of hermaphroditic plants to produce zygotes after self-pollination. It is characterised by failure of any of these stages: pollen germination, growth of pollen tube, fertilisation & embryo development.
What could cause self-incompatibility?
- Could be due to variations in flower structure e.g. diff in length of stamen & style. These variations are governed by self-incompatibility genes
- Could also be due to genes for self-sterility present in some plants.
How does genes for self-sterility lead to self-incompatibility?
Most often these genes have multiple alleles. A plant carrying one allele, say ‘s1’ is unable to pollinate another plant with the same allele (s1) as the pollen grain fails to germinate. In cases where pollen tube grows, fertilisation & seed formation doesn’t happen. Ensures that plants don’t produce seeds if they are self-pollinated or pollinated by genetically similar plants.
What happens soon after fertilisation?
Soon after fertilisation, a series of changes occurs. Most of parts of flower dry & fall off. Inside ovule, zygote divides mitotically to form embryo while triploid cell develops into endosperm. The wall of ovule becomes seed coat enclosing embryo & endosperm. The ovary forms the fruit.
Why is seed dispersal important?
If all the seeds fall close to the parent plant, there will be intense competition for resources like water, soil and sunlight. To prevent this, seeds must be dispersed to new areas.
What are the different methods of seed dispersal?
Seed dispersal can happen via wind, water or animals.
What are the adaptations to seeds that are dispersed by wind?
Wind-dispersed seeds = light & have a number of adaptations e.g. wings or hair that help them to be carried by wind. E.g. dandelion (Taraxacum officinale), seeds of many grasses, seeds of drumstick (Moringa oleifera) & seeds of maple (genus Acer).
What are the adaptations to seeds that are dispersed by water?
Seeds dispersed by water = buoyant e.g. water lilies (genus Nymphaea) & coconut (Cocos nucifera). The fibrous covering of coconuts & specialised structures called aril in water lilies help these seeds to float.
What are the adaptations to seeds that are dispersed by animals?
- Animals may feed on fleshy fruits, & toss the seed some distance away.
- Animals may eat fruit along with seeds. Seeds pass through digestive system undigested & are thrown out as faeces.
- Animals e.g. squirrels & chipmunks may collect & hoard seeds in diff places.
- Some seeds have hooks & spines that cause them to attach to skin & fur of passing animals.
What is germination?
Germination = development of seed, which begins with uptake of water of seed & is completed when radicle emerges from seed. It only occurs when conditions are suitable for growth of plant.
What happens if the conditions aren’t suitable for germination?
Seed remains dormant, a condition where all metabolic activities are slowed down. Period of dormancy varies from one plant species to another. Some seeds, e.g. magnolia, can remain dormant for only a few weeks; others, e.g. seeds of desert wildflowers, can remain dormant for years.
What are the conditions required for germination?
- Water, as it hydrates & thereby activates metabolic reactions of embryo.
- A favourable temperature. Most seeds germinate best at temperatures 25 °C to 30 °C. Very low temperatures or very high temperatures prevent germination.
- Oxygen = Shortly before seed coat ruptures, embryo begins to respire. Cellular respiration & other metabolic activities of growing embryo require oxygen.
What are the changes between germination & post-germination that lead to growth & development of embryo?
- Imbibition of water - dry seeds imbibe water & swell up, causing seed coat to rupture.
- Respiration - metabolic activities are suspended or reduced during dormancy. Soon after imbibition of water, various metabolic processes resume & rate of respiration of embryo increases.
- Mobilising food reserves - Until it becomes self-supporting, embryo depends on food reserves present in endosperm. These reserves are in form of carbohydrates, proteins & lipids which need to be mobilised & translocated. Studies show that in cereals, following the uptake of water, the embryo produces gibberellins. These hormones cause release of enzymes that break down stored food reserves converting them into sugars, amino acids & fatty acids. Food is then absorbed by cotyledons & transported to growing embryo.
- Development of embryo axis into a seedling - Rapid growth results in emergence of primary root or radicle in most species (marking the end of germination). It is then followed by emergence of plumule (or the shoot). At this point baby plant is known as seedling. Shoot develops green leaves which, in turn, begin to synthesise food.
- Effect of light on seed germination - Once plumule has emerged, light plays an important role in orientation of seedling. When plumule emerges it is bent over to protect delicate growing tip. Straightening of plumule occurs on exposure to light.
