Sexual Reproduction in Plants Yr 7 PDF

Sexual reproduction in plants What do you know already? Are there different methods? Are there different steps? What plant cell types or organs are used / needed?  Learning Objectives Learn the parts of a typical flower Understand what pollinatio...

Sexual reproduction in plants What do you know already? Are there different methods? Are there different steps? What plant cell types or organs are used / needed?  Learning Objectives Learn the parts of a typical flower Understand what pollination is Understand what fertilisation is Understand how flowers rely on animals for pollination, and that the process is of mutual benefit to both organisms Understand germination Understand the life cycle of flowering plants Can you label any of these?  Plant Reproduction Flowers are the reproductive organs of a plant, allowing them to undergo sexual reproduction. Fertilisation occurs when the nuclei of male and female sex cells (gametes) fuse (join together) to form a zygote. Male sex cells are the pollen grains. Female sex cells are the eggs.  Plant Reproduction Male reproductive organ = stamen. These are made up of filaments and anthers. They produce the male gametes, pollen. Female reproductive organ = carpel. These are made up of the ovary, style and stigma. The ovary produces the female gametes, eggs/ ova Structure of A Typical Flower Structure of A Typical Flower  Plant Reproduction (Notes) Flowers are the reproductive ________ of a plant, allowing them to undergo _______ reproduction. Fertilisation occurs when male and female g__________ f____ to form a zygote. Male reproductive organ = ________. These are made up of the ________ and _______. They produce the male gametes, p_______. Female reproductive organ = ______. These are made up of the _____, _____ and _______. The ovary produces the female gametes, eggs (ova). Help words: Carpel, pollen, fuse, stigma, sexual, anther, style, organs, ovary, stamen, gametes, filament Extension: go to this website and look at the diverse range of flower types https://www.theseedcollection.com.au/blog/Guide-to-the-Different-Flower-Types  Plant Reproduction (Notes) Flowers are the reproductive organs of a plant, allowing them to undergo sexual reproduction. Fertilisation occurs when male and female gametes fuse to form a zygote. Male reproductive organ = stamen. These are made up of filaments and anthers. They produce the male gametes, pollen. Female reproductive organ = carpel. These are made up of the ovary, style and stigma. The ovary produces the female gametes, ova.  Notes Draw and label a flower Structure Function Holds up the stigma Female reproductive organ of the flower Sticky to catch pollen grains Protect the flower when developing in a bud Colourful to attract pollinating insects Contain ovules Male reproductive organ of the flower Where pollen grains are produced Contains the female gamete Hold up the anthers Secrete nectar to attract pollinators Male gamete Structure Function Male reproductive organ of the flower Female reproductive organ of the flower Where pollen grains are produced Hold up the anthers Male gamete Contain ovules Holds up the stigma Sticky to catch pollen grains Contains the female gamete Protect the flower when developing in a bud Secrete nectar to attract pollinators Colourful to attract pollinating insects Structure Function- Notes Stamen Male reproductive organ of the flower Carpel Female reproductive organ of the flower Anther Where pollen grains are produced Filament Hold up the anthers Pollen Male gamete Ovary Contain ovules Style Holds up the stigma Stigma Sticky to catch pollen grains Ovule Contains the female gamete Sepal Protect the flower when developing in a bud Nectar Secrete nectar to attract pollinators Glands Petal Colourful to attract pollinating insects What is the bee doing and why is it doing it? Is the bee considered a pest by the flower? If not, why not?  Insect pollination How do flowers attract insects? Why does the insect reach into the flower? Where does the insect ‘ideally’ leave the pollen in the 2nd flower?  Pollination Definition – the transfer of pollen from anther to stigma of a flower. (Transfer of male sex cells to female sex cells) If this occurs within the same flower it is self- pollination. If it occurs between different flowers it is called cross-pollination  The insect is lured to the flower by the colourful petals, the scent and the nectar and pollen which is used as a food source. As the insect collects the nectar at the base of the flower the pollen on the anthers, rubs off onto the insect’s body.  With pollen on its body, the insect goes to a second flower, looking for more nectar. As it enters the flower it brushes past the stigma, pollen is left on the stigma because it is sticky. Pollen has now been transferred from the male part of the flower (anther) to the female part of the flower (stigma)  Female bees honey bees, and bumblebees have specialized structures called pollen baskets used for temporarily storing collected pollen so it can be transported back to the nest/colony.  As the bee visits flowers, she accumulates pollen all over her body. She uses her legs to aggregate the pollen and transfer it to her pollen basket. It may look as if a bee simply has hairy legs, but some of those hairs are actually combs and brushes used for transferring pollen. The pollen is combed, pressed, compacted, and transferred to her pollen basket. Honey and/or nectar is used to moisten the dry pollen so it will stay in place.  Pollination Notes Definition – the transfer of pollen from ______ to ______ of a flower. (Transfer of male sex cells to female sex cells) If this occurs within the same flower it is called _____ pollination. If it occurs between different flowers it is called ______ pollination this results in more variation due to different combinations of DNA.  Pollination (Notes) Definition – the transfer of pollen from anther to stigma. (Transfer of male sex cells to female sex cells) If this occurs within the same flower it is self-pollination. If it occurs between different flowers it is called cross- pollination this results in more variation.  Are insects the only animals that can pollinate flowers?  Animal pollination Different flowers are adapted for the animals that pollinate them. For example bees notice yellow and orange flowers. Nocturnal animals like bats find scented flowers easily. Birds are attracted to red flowers. The smallest flower is the size of a sesame seed (Wolffia) and the largest is the jungle flower Rafflesia arnoldii which can be up to 3 feet across. It smells like rotting meat to attract flies!  Rafflesia plant in Indonesia Here's a Lepto Bat approaching a saguaro flower. The flower has a strong odour to attract the bats and the big white flower makes it easy for them to see it even with only starlight to guide them. Most flowers pollinated by bats grow at the top of the plant, or on branches so they are easy for the bats to find and get to. Lepto bats can hover, but only for a second or two, so they need to take good aim when they approach the flower. (They wouldn't want to miss and hit those nasty spines!) The saguaro flower is a perfect fit for a Lepto's head! It sticks its face right into the flower to get the sweet nectar. The nectar pools right at the base of the flower, so the Lepto has to stick out its long tongue to get to it. When fully extended, its tongue is longer than its head! While hummingbirds derive some nutrition from eating small insects and spiders, the average hummingbird requires the nectar of 1000 flowers each day. Australian honey possums  Many plants have a mutualistic relationship with animals. How do you think this applies to insect pollination of flowers?  The bee and the flower Bees fly from flower to flower gathering nectar, which they make into food, benefiting the bees. When they land in a flower, the bees get some pollen on their hairy bodies, and when they land in the next flower, some of the pollen from the first one rubs off, pollinating the plant. In this mutualistic relationship, the bees get to eat, and the flowering plants get to reproduce.  For interest Plants are very clever… they have co-evolved over a long time with animals and have thus developed some interesting ways to ensure they get pollinated…. What is this bee trying to do? (It is not trying to get pollen or nectar)  Orchids use bizarre devices to ensure they reproduce – including impersonating the sex organs of a female bee https://www.theguardian.com/science/2011/ oct/09/orchid-sex-botany-ziegler-pollan  A male solitary bee, is engaged here in pseudocopulation. Photograph: Christian Ziegler/Minden Pictures  Some flowers look like a bee or wasp—complete with the requisite shape, colours, markings and hairs. They also exude a scent that simulates the pheromones produced by receptive females. When the male lands on the flower, it attempts to copulate with it. In the process, the flower deposits pollen on the insect's head, to be carried and placed on the next flower they visit. Why is pollination important for humans?  Many crops are dependent on, or benefit from, visits from pollinators. The economic value of pollinators is millions per year.  Do all plants need animals for pollination?  No Some plants use wind pollination Some plants do not have flowers and reproduce using seeds in cones or spores  Plants using wind pollination need adaptations in the flowers 1. adaptations for getting rid of pollen into the wind from the first flower 2. catching pollen from the wind for the second flower. Grasses, cereal crops, conifers and many other trees are wind pollinated Features of WIND POLLINATED flowers How are these structures adapted to function? small petals, often brown or dull green - no scent – no nectar – lots of pollen - pollen is light and smooth – anthers hang outside the flower - stigma hangs outside the flower – stigma is feathery or net like - Features of WIND POLLINATED flowers small petals, often brown or dull green - no need to attract insects no scent - no need to attract insects no nectar - no need to attract insects lots of pollen - because most does not reach another flower pollen is light and smooth - so it can be blown in the wind anthers hang outside the flower - to release pollen into the wind stigma hangs outside the flower - to catch the drifting pollen stigma is feathery or net like - to catch the drifting pollen in the air Features of INSECT POLLINATED flowers large, brightly coloured petals - to attract insects often sweetly scented - to attract insects usually contain nectar - to attract insects moderate quantity of pollen - less wastage than with wind pollination pollen often sticky or spiky - to stick to insects anthers firm and inside flower - to brush against insects stigma inside the flower - so that the insect brushes against it stigma has sticky coating – so the pollen sticks to it Notes- WIND POLLINATED flowers are different to insect pollinated flowers: small dull petals, no scent, no nectar pollen is light - so it can be blown in the wind stigma is feathery or net like - to catch the drifting pollen in the air What happens after pollination?  Fertilisation After pollination, the pollen grain grows a pollen tube The tube digests its way through the style and into the ovary through a hole called the micropyle The male nucleus travels down through the pollen tube, into the ovary and an ovule The male and female nuclei fuse and form a zygote The zygote (one cell) will divide to form an embryo There are multiple ovules and eggs which can be fertilised from different pollen grains Pollen Grain Pollen tube Ovary Ovule Micropyle  What happens to the flower after fertilisation? Have you ever eaten a plant’s ovary?!  Fertilisation à Fruits The ovule forms a seed with the embryo inside it. The ovary forms the fruit.  We know that apples, strawberries, peaches and oranges are fruits but are these fruits or from fruits? Or are they vegetables? 1. avocado 2. potato 3. broad bean 4. carrot 5. walnut 6. sweetcorn 7. tomato  1. avocado 2. potato 3. broad bean 4. carrot 5. walnut 6. sweetcorn 7. tomato  A walnut is the edible seed in the fruit  In scientific terms, the word 'fruit' has a slightly different meaning to its everyday usage. Botanically, fruits grow from the flowers of plants and contain seeds, while vegetables are the plant’s other parts. Yet, from a culinary perspective, fruits are sweet or tart, while vegetables are mild, savory, or bitter.  As well as familiar edible fruits acorns, peas, holly berries and sycamore 'helicopters' are all classed as fruits. Observe a strawberry or a blackberry. These fruits are formed from a single flower that contained many carpels.  Observe a pineapple. This fruit is produced by the fusion of many flowers. Can you see each individual fruit?  Life cycle of a flowering plant Apple tree makes blossom Flowers are pollinated Fertilisation occurs Flower dies Fruit forms from the ovary Seeds form from the ovules Embryos are in the seeds Embryo grows into new plant Plant matures into an apple tree Apple tree makes blossom  Fertilisation and fruit formation The pollen grains on the s_______ start to grow a p_______ t________ down the s______ to the o______, carrying the pollen n__________ down. Egg cells are found within o______ inside the o______. The pollen nucleus then f______ with an egg cell nucleus- this is called f___________. The ovary now becomes a f______. The ovule now forms a s_____ with the embryo inside it. Seed dispersal and Germination  Why do plants disperse / spread their seeds? What methods of seed dispersal are there? What conditions are needed for germination? What happens to the seed during germination? Seeds  Seed dispersal If all the seeds produced by a ‘mother’ plant begin to grow in the same area there would be too much competition. To avoid this plants disperse their seeds The seed can be dispersed safely because it is a protective structure for the embryo. Animal dispersal: Water dispersal Wind dispersal Another but less common method is ‘explosion’  Water dispersal of coconuts  Juicy fruits dispersed by animals Each blackberry is made up of many separate sections, each containing a single seed They are collected and eaten by many animals, including humans The juicy part of the fruit is digested, but the hard seeds pass through into the animal's droppings  Juicy fruits dispersed by animals Holly Each holly berry contains a single seed The berries are mainly dispersed by birds Since birds can see colour well, holly berries are coloured red so that they contrast with the glossy green leaves More animal dispersal Acorns Each acorn contains a single large seed Acorns are collected and stored for winter food by small mammals such as squirrels and mice. Many mammals do not see well in colour, so seeds do not need to be brightly coloured to attract them More animal dispersal Horse chestnut The fruit of the horse chestnut is actually the prickly green case This splits to reveal the seed of the horse chestnut tree - the conker Ripe conkers are carried away from the parent tree by small mammals and used for winter food  A cleaver is a spreading plant which has 'sticky buds' - small round fruit with hooked bristles which cling to the fur of passing animals The stems and leaves also have these bristles, so animals may pick up long trailing bits of stem with many fruits  Poppy Self dispersed The fruit of the poppy is shaped like a 'pepperpot', with a ring of holes near the top It is arranged at the top of a stiff but springy stem When an animal walks past, or the plant is blown by the wind, the stem is bent back, releasing the small black seeds through the ring of holes Sycamore Winged fruits dispersed by the wind Sycamore fruits are arranged in pairs, each with an off-centre wing After the two wings have separated, the fruit spins as it falls, carrying it further from the parent tree  Wind dispersal: Milkweed, dandelion  Dandelion The seed head of the dandelion is made up of many individual 'parachutes', each attached to a single fruit and seed The 'parachute' keeps the seed in the air, allowing it to be carried away on the breeze from the parent plant  Himalayan balsam Self dispersed - exploding fruit As the fruit ripens, pressure builds up inside the fruit as the cells swell When a passing animal brushes against the plant, the ripe fruit splits open explosively, and scatters the seeds widely  Seed dispersal notes 1. Why are seeds dispersed? 2. Describe some different methods of seed dispersal with examples  Seed dispersal- answers why are seeds dispersed? If all the seeds produced by a ‘mother’ plant begin to grow in the same area there would be too much competition. To avoid this plants disperse their seeds The seed can be dispersed safely because it is a protective structure for the embryo. list four methods of seed dispersal Animal dispersal: eg seeds with hairs or hooks that catch on animal fur eg cleavers, sandbur Seeds inside fruits eg bananas, acorns, blackberries, are dispersed in faeces after the fruit is eaten by an animal Wind dispersal eg dandelion, sycamore, Water dispersal eg coconut Explosion – (less common method) eg poppy, Himalayan balsam  What happens after seed dispersal if the environmental conditions are favourable?  How does the embryo (in the seed) have energy to grow if it has no leaves and cannot photosynthesise?  Germination Fusion of the pollen nucleus and egg cell nucleus creates a zygote. The zygote develops into an embryonic plant with small roots and shoots. The other contents of the ovule develop into a food store. The embryonic plant can use this food store as it grows during germination. Eventually the plant will have it’s own leaves and can make food by photosynthesis The seed develops from the ovule, it contains the embryo and is surrounded by the maternally derived seed coat. The function of the seed is to protect the embryo, to sense environmental conditions favourable to germination and to nourish the germinating seedling.  Skill You need to be able to draw the internal structure of a seed  Conditions for Germination Germination requires: the WOW factor 1. Warm temperature 2. Oxygen for respiration 3. Water to rehydrate the dry seed Once the seedling is able to photosynthesise it can make its own ‘food’, and germination is over. Note that light is not needed for germination.  Germination Notes 1. List each of the 3 main factors needed to stimulate germination of a seed  Investigating germination Design an investigation to see the effect of temperature on germination IV- temperature eg 5,10,15,20,25,30 ℃  DV- time taken for shoot or first leaf to emerge- are you going to observe the seeds continuously? Every hour? Every day? DV- number of seeds with 1 or more leaves, or a shoot of 1mm or more (seeds observed every day at 9am and 9pm).  CVs type of water and volume of water given to each plant (each day?), plant species, type of soil (in order to control pH and nutrients), atmospheric oxygen concentrations,  Repeats- plant at least 10 seeds at each temperature more reliable data easier identification of anomalies  Reproduction in plants Sexual reproduction is very energy consuming but it has the benefit of producing variation in the offspring Asexual reproduction does not lead to variation but has other benefits  Plant Reproduction If the environment has been stable for many generations, (e.g same water availability, nutrient and light levels) then because the parent survived in those conditions, identical offspring produced by asexual reproduction will survive too. Sexual reproduction brings together DNA from two different parents and creates variety in the offspring, in a stable environment, variability in the population is not essential to the survival of the species. But diversity and variability in a species is needed to adapt to and evolve in a changing environment. Eg in a drought if some of the offspring made from sexual reproduction can tolerate drier conditions then not all of population will die out