Reproduction in plants

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Reproduction in plants




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Presentations text content in Reproduction in plants

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Reproduction in plants

Arthur and Kelvin

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-> Flowering involves a change in gene expression in the shoot apex.-> The switch to flowering is a response to the length of light and dark periods in many plants.-> Most flowering plants use mutualistic relationship with pollinators in sexual reproduction-> Success in plant reproduction depends on pollination, ,fertilization and seed dispersal.

Understandings

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Flowering and gene expression

When a seed germinates, a young plant is formed that grows root, stems and leaves and these are called

vegetative structures

, which indicates that it is currently in

vegetative phase

.

Flowers can only reproduce until something stimulates the plant to change from the vegetative phase into

reproductive phase

and the stimulus is a change in the length of light and dark periods.

Once the flower is mature, it will spread it’s pollens (

Pollination

) by

mutualism

, which will trigger

fertilization

.

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Short day plant and Long day plant

Chrysanthemums: Irises:

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Differences

Short day plant flowers when the night is longer and these plants ONLY flower in fall or winter, since days are getting shorter and shorter.

Short day plants will not flower if some artificial light is shined onto the plant for a few minutes during night as they require a consolidated period of darkness before floral development can begin.

Moonlight or lightning does is not enough to interrupt the flowering of short day plants.

Long day plants flower around spring or summer and they require more contact with light.

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Photoperiods and flowering

The switch in plants respond to the length of light in

darkness periods

which affects the flowering of plants

Long-day plants flower bloom in summer when the nights are short enough and short-day plants flower bloom in autumn when the nights have become long enough

Summer (shorter) and Winter (longer) have different night periods

Plants contain

phytochromes

to measure the length of dark periods

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Phytochrome

Phytochrome is a pigment in leaves that plants are used to detect the length of dark periods at night

Photoreceptors (light sensitive)

There are two forms of phytochrome Pr and Pfr

Pr and Pfr switches forms according to the light wavelength

(switch is important for plants to detect night periods)

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Hit by red Light (Light wavelength of 660 nm~)

Hit by far-red Light (Light wavelength of 730 nm~)

The shift from night time to day time

The shift of day time to night time

Sun light contains more 660 nm than 730 nm wave length so in normal sunlight phytochrome is rapidly converted from Pr to Pfr

Pr is more stable than Pfr, so in darkness, Pfr very gradually changes back into Pr

Receptor proteins are presented in the cytoplasm to which Pfr but not Pr binds

Active Form of phytochrome

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Long-day plants

Have large amount of Pfr remains at the end of the night to bind to the receptor

Promotes transcription of genes needed for flowering

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Short-day plants

Receptor inhibits the transcription of the genes needed for flowering when Pfr binds to it

Since after long night, Pfr gradually changes into Pr, there are limited Pfr left for binding with the receptor

Inhibition fails and the plant flowers

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Pollination

Pollination is the transfer of male parts of a flower to the female part of the flower (Stigma).

Each pollen has around 5000 sperm.

Pollinators

such as bees are attracted because they can gain food (nectar) and the pollen will be able to attach itself onto the bees and potentially land on a stigma. This double-beneficial relationship is called

Mutualism

.

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Bee covered in pollen

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Fertilization

Fertilization occurs once a pollen has landed on the stigma and a reaction called the

enzymatic reaction

will create a tube (

Pollen tube

) within the stigma that allows the sperm from the pollen to swim to the ovary.

The ovary is located inside a small rounded structure called an ovule.

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Diagram of flower

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Seed dispersal

Some plants do not have pollens to spread and an example is the coconut tree.

Coconut trees lives near rivers, lakes and coastlines because once the seed is mature, it will fall off the tree and down towards the water source, which will potentially wash it ashore to a new location.

The seeds are ONLY released when the outer shell of the coconut

decays

or is

digested/broken

down by animals.

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Picture of coconut tree

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Keywords

Vegetative phase

- The phase before reproductive phase and can be stimulated into the reproductive phase when the stimulus is present (Light). This can be spotted when there are vegetative structures present.

Pollinators

- Animals that help transfer the pollen. Examples are honey bees and hummingbirds.

Mutualism

- Both organisms receive benefits. Example is when the honey bees or hummingbirds obtain nectar from the flower and help spread the pollen.

Enzymatic Reaction

- A reaction that only occurs once a pollen lands on top of the stigma and it creates a tube called the pollen tube. The pollen tube allows the sperm from the pollen to swim towards the ovary.

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