Lesson video

Welcome to this lesson from the unit "Plant Growth and Development".

The title is "The Effects of Gibberellins and Ethene on Plant Growth and Development".

So we're gonna be looking at these two chemicals, plant hormones, certainly ethene acts as a plant hormone, gibberellins and ethene, and how that they stimulate growth, how they are involved in fruit production, flower production, germination, ripening, many processes that are involved in plants.

My name's Mrs. Barnard, and I'm going to be taking you through today's lesson.

So by the end of today's lesson, you should be able to describe the effects of gibberellins and ethene on plant growth and development.

And our keywords for today's lesson are: gibberellins, ethene, ripening, and germination.

If you'd like to write down the definition of these, then just pause the video, otherwise we'll be going through them as we go through today's lesson.

So our lesson today is in two parts.

The first part is looking at gibberellins, which is a plant hormone, and the effects that it has on plants, and ethene, which is actually a gas that has lots of other uses, but in plants, it does act as a plant hormone as well.

So let's get started with the first part of today's lesson, which is gibberellins.

So plant hormones are chemical molecules, and they control important processes in plants like germination, so that's when a seed germinates for a shoot to come out, flower opening, fruit ripening, and tropisms. Now tropisms is the growth of plants in response to stimuli like light or gravity.

So important plant hormones include auxins, which you may have learned about before, gibberellins and ethene.

So just a little bit of reminder about auxins.

They are dealt within a separate lessons.

So auxins control the growth of plant towards and away from a stimulus, and those are called tropisms, so negative and positive tropisms. So for example, here we've got a shoot growing towards the light and against the direction of gravity.

So even though this plant has been turned on its side, it's growing upwards towards the light to try to get the light it needs for photosynthesis.

And in this example, we've got roots that are growing in the same direction as gravity.

So we've got positive gravitropism there, and of the first one, we've got positive phototropism there.

And it's auxins that control that.

So gibberellins, so gibberellins are plant hormones, and they're responsible for quite a lot of things that are involved in growth and development.

They've got a really important role in seed germination and the development of seedling plants.

So we can see here we've got our seed, and in the seed at the bottom, this is a pistachio seed, so you might have had them as pistachio nuts, but if you soak them, you could do this yourself, if you soak them and cut them open, you can actually see inside there's a little plant embryo there at the bottom that's labelled.

So seeds are held in a state of dormancy.

So you might have seeds in your cupboard, for example, that are dried, and they don't germinate straight away, because they need the right conditions in order to start to germinate.

So they will stay in this state of dormancy until the environmental conditions are suitable for germination.

And when those environmental conditions are suitable, it's gibberellins that initiate that germination process.

And you might have had a chance to germinate seeds before in previous lessons, so here's a picture of some cress seeds that are germinating.

And once germination has begun, there are increasing levels of gibberellins, and they cause the cells in the embryo, so that little picture that we just saw before inside the seed, they cause those cells to start to divide and differentiate, which means turn into different types of cells that will form the shoots and the roots, allowing the little plants, the seedlings, to grow first and then into plants.

So gibberellins are also involved in flower and fruit formation.

So they'll cause fruits to form, and also to increase in size.

We can see that at the example of the raspberry fruit here.

But they also cause flowering.

Now sometimes they cause flowering when a plant is limited in terms of its environmental conditions.

So for example, the amount of water it can get, or the space that it's got, and it will simulate flowers to grow quite quickly in order that pollination can take place before the plant dies.

So that's quite an interesting process that it's involved in.

And you might have seen that with sort of things like herb plants if you grow those in your garden or you're in your kitchen.

So time for a quick check.

Gibberellins control growth towards or away from a stimulus.

So I want you to decide whether you think that is true or false, and I want you to decide which of the statements below best justifies your answer.

So pause the video while you do that, and then we'll come back, and we'll see if you've got it right.

Okay, so gibberellins control growth towards or away from a stimulus.

This is false, and the reason is because it's auxins.

Auxins control elongation, which leads to directional growth.

Okay, that's not the role of gibberellins.

So if you've got that right, well done.

Next one, which of these following statements are true for the roles of gibberellins? So out of those four, select which ones you think gibberellins are involved in.

Pause the video, and then we'll see if you've got it right.

Okay, so the correct answers are promotes flowering, yes, it does, promotes fruit formation, it does, fruit ripening, it does not, and it initiates germination.

So lots of involvement in plant processes there for gibberellins.

So if you've got those right, then well done.

Let's move on.

So gibberellins are used in agriculture and horticulture to control plan growth.

Now what do those two words mean? So agriculture is growing crops or raising livestock for use by humans.

So agriculture is how we get our food, okay? Now horticulture can involve food, 'cause it can be getting fruits, but generally on a smaller scale like garden fruits, but on vegetables, but also flowers, gardening, okay, that sort of thing, that's horticulture.

So gibberellins can be used to promote germination.

So farmers can apply these to seeds to ensure that they germinate at the same time, because otherwise you are waiting on the environmental conditions to be correct.

And what you want is you want all of your seeds to germinate at the same time, and sometimes you want 'em to germinate even if the conditions haven't been exactly the way that the seed would want them prior to when you want germination to start.

So this allows germination to take place without the conditions that are normally required beforehand, which might mean that it needs to be either cold beforehand, because then that stimulates them to know that they're out of the winter, or it might be that there needs to be enough water, or a specific temperature in order for them to germinate.

So it means it gets them all on the same level playing field and all of those seeds can germinate without the correct conditions.

It also means that the crops will grow at similar rates, not exactly the same, but if they grow at similar rates, it means it's much easier for them all to be harvested at the same time.

Gibberellins can also be used to promote flowering.

And if you give a plant lots of gibberellins, you can make flowers grow quite big.

So plants that normally flower when days are longer can be stimulated to flower earlier.

So that means that you can get plants grown in different seasons that wouldn't naturally grow in those seasons, or if the conditions have less light than they're used to, or if the conditions have lower temperatures.

So we're trying to promote flowering outside of the natural conditions that those plants would normally flower in.

So that will lead to flowers growing more quickly, and also might cause 'em to grow larger.

So if you've got flowers growing more quickly and larger, it means that the farmers can make more profits, because they've got more flowers growing in a given amount of time, they've got the types of flowers that people will want to buy growing in that amount of time.

So therefore this is why it's widely used in agriculture and horticulture.

So flowering also has an impact on the rate of fruit growth.

So remember flowers are involved in reproduction, because we have pollination between the flowers which transfers the pollen from one flower into another, which then will transfer down to the ovary to an egg, and then it forms a seed, okay? And then that's when your fruit will form.

But gibberellins are used to produce seedless fruits.

That means that we can promote the production of fruit without waiting for pollination to have taken place.

Now seedless grapes are sprayed with gibberellins also to increase their size.

We both get fruit formation without flowers, and without seeds, and we get an increase in fruit size.

So you can see why gibberellins are so important in the production of grapes.

And we eat a lot of grapes in this country.

It increases the profit for farmers, because it means that they can grow faster, 'cause we're not waiting for all the processes to take place before they grow, but also it provides the consumers with what they want.

So consumers want large grapes that are seedless, and therefore the farmers are gonna be able to make more profit from that.

So time for a quick check.

Can you select the agricultural uses of gibberellins? And you've got three to choose from.

So pause while you decide, and then I'll let you know if you've got it right.

Okay, let's see if you've got these ones right then.

So A, it stimulates fruit production.

Yes, it does.

And C, it stimulates germination.

Yes, it does.

It doesn't stimulate root growth, okay? Auxins can be used for that.

So time for a quick practise task.

So blueberries and Calla lily plants, so we've got some images of those there, can be bought at the supermarket.

Now using your understanding of gibberellins explain how farmers can increase the profits that they make from these two products.

So one's a fruit and one's a flour.

And how would farmers use gibberellins to increase profits from these two products? So pause the video while you write about this, 'cause it'll be a bit of extended writing, and then we'll have a look at some model answers after.

Okay, let's see how you got on then.

So how can we use gibberellins to make some profit for farmers on these two products, blueberries and Calla lily plants.

So gibberellins can be used to stimulate the germination of blueberry and Calla lily plants so that they start to grow without having been exposed to the usual conditions beforehand, and also in a wider variety of different conditions.

This means that more plants can be grown, and they can be harvested at the same time to reduce costs and increase profits.

Blueberry plants can also be sprayed with gibberellins to promote large seedless blueberries to grow, and on Calla lilies to promote flowering and to increase flower size.

This makes both of these products more appealing to the consumer, leading to higher sales and increased profits.

So if you've got a number of those ideas in your answer, well done.

If you want to add it in, now is the time.

But it is interesting to find out how just using one hormone can make such a difference.

So now we're gonna move on to the second part of today's lesson, which is ethene.

You may have heard of ethene before, because ethene is a hydrocarbon gas, it's an alkene, and it's made by a plant at various points of its lifecycle, you might have heard about it in chemistry lessons, but it also acts as a plant hormone.

It's involved in the control of cell division, so mitosis, during plant growth, and also in the dropping of leaves.

Ethene is also produced as fruit matures.

It acts as a plant hormone to activate that fruit to ripen.

So you've got an image here of some tomatoes as they're ripening.

So when they're grown, you might know this, they start green, and then they get orangey until they get towards red.

So ripening is the process a fruit goes through to make it ready for eating, so it becomes sweeter and softer.

And you might see this example just in your kitchen that bananas release this chemical, ethene, that causes fruit ripening, but it can actually encourage the ripening of fruit that's in the bowl with it.

So certain fruits, particularly soft fruits like pears, for example, will ripen really quickly if they've got banana next to it, so often people will keep bananas separate in the kitchen from the rest of the fruit.

Although, you can also use them to speed up ripening.

So if you have some pears that aren't very ripe, you might want to put the bananas next to them.

Or avocado, if you have some avocado that's not very ripe, you might wanna put them in a bag with some bananas, and that can speed up the ripening of them as well.

So in the food industry, fruit is often picked unripe, and then it's transported.

I think much of our fruit is transported across the world.

So it's often picked before it is actually ripe.

Because fruit is firmer, so it's less likely to be damaged, I think you know that probably from the fruit that you have looked at, that when it's softer it's more likely to be damaged.

And because it's transported large distances across the world, it's really important that farmers can get as much fruit to where it needs to go to sell without it becoming damaged.

Also, if it's on quite a long journey, you don't want the fruit to ripen on the journey, so by the time it gets to the other end, it's over ripe, and nobody wants to buy it.

So ethene is used in the food industries to ripen the fruits at the point when it is required.

And this often takes place during transportation.

So you have these big ships that have these refrigerated containers on them, and the fruit is kept in there, in those refrigerated containers, to stop ripening from taking place.

And at the point that they do want the fruit to start ripening, then they will pump in ethene gas in order to encourage ripening to start to take place.

So that will reduce the amount of fruit that is spoiled or over ripened.

Lots of people don't like eating fruit that is too ripe like bananas, for example.

And thus that means that the farmers will get more profits 'cause there's more fruit that gets the to other end that's saleable.

So the production of the ethene by the fruit can be inhibited, 'cause you might think, oh well, they might be producing the ethene anyway, so that can actually be inhibited, and that'll delay the ripening of fruits.

So chemicals that prevent ethene from being produced can also be pumped into those containers, and also they can remove the ethene.

So they've got a way of removing the ethene from around the fruit.

So just really reducing the amount of ethene that's anywhere near that fruit until they actually need it to ripen.

So these are some tomatoes that would be picked in this green colour, and then they would be transported, and then they would be ripened before that they were ready to be sold.

So time for a quick check.

Ethene activates fruit ripening.

Is that true or false? And once you've decided, could you have a look at the statements below, and see which one do you think best justifies that answer? So pause the video while you do that, and then we'll come back and we'll check on your answer.

Okay, so ethene activates fruit ripening.

That is true.

And the statement that best justifies that is the first one, it's made naturally in fruit, and it can be applied artificially to unripened fruit.

So if you've got that right, then well done.

So let's move on to a task now.

So we've got a confidence grid here, and for each of these statements I want you to decide whether you think it is correct or incorrect.

And once you've decided whether it's correct or incorrect, how sure are you, are you sure it's correct, or do you think it's correct? Are you sure it's incorrect, or do you think it's incorrect? Okay, so have a go at doing that, and then when you come back, we'll look at the correct answers before then we move on to a second task using that information.

Okay, so let's have a look at the correct answer for these.

So ethene is produced naturally by fruit.

That is correct.

Ethene can be applied to fruit to prevent them from ripening.

That is incorrect.

Ethene is a gas.

That is correct.

And ethene can be applied to fruit during transportation.

That is also correct.

So what I'd like you to do now is alter or expand on each statement to add detail about the role and commercial use of ethene.

So these were the statements.

So I would like you to alter them, or expand on them, to make them correct with more scientific detail.

So pause the video while you do that, and then we'll have a look at some model answers.

Okay, let's have a look at these together then.

So ethene is produced naturally by fruit.

It is produced as the fruit is forming, and it activates ripening.

Ethene can be applied to fruit to prevent them ripening.

This is incorrect.

Ethene can be applied to activate ripening.

Ethene is a gas.

It is and it acts like a plant hormone.

And ethene can be applied to fruit during transportation, and this is so that they can be picked unripe, and then ripened before sale.

So if you finished your sentence with something along those lines, that's good, make any corrections, or you might have put some extra detail on.

That's brilliant.

So it's time for our final task.

And here we have Aisha and Jacob.

And Aisha and Jacob are discussing the drawbacks of ethene use in commercial fruit production.

So what I'd like you to do is read what they've said.

So Aisha says, "Ethene is an artificial chemical and should not be applied".

And Jacob says, "Using artificial ethene will be very costly".

So what I would like you to do is write an explanation for why it is beneficial for businesses to use artificial ethene in fruit production, 'cause they've obviously stated a couple of drawbacks.

So we're stating the other side of the argument.

So pause the video while you do that, and we'll come back and we will have a look at your answer.

Okay, let's see if you got on well with that.

Okay, so we want to find some benefits of using ethene.

So Aisha and Jacob have come up with the drawbacks.

So Aisha said it's an artificial chemical and it should not be applied.

And Jacob has said using artificial ethene could be very costly.

So the benefits.

Fruit is grown all over the world, so it must be transported.

And if it is picked when it is not ripe, then it will be firmer, so it's less likely to be damaged or over ripe by the time it gets to its destination.

So you will have less wasted food.

Ethene can be used during transportation to ripen the fruit nearer to the destination.

This means that more of the fruit that's picked can be sold, so it will increase profits, but it also increases food availability, and it reduces waste.

So again, if you've got some words that affect, some arguments that affect them, that's good.

If you need to make any corrections, then please do so.

But otherwise, well done.

And now that brings us to the end of today's lesson, which is the effects of gibberellins and ethene on plant growth and development.

So gibberellins are plant hormones that cause plants to produce flowers and cause seed germination.

Plant breeders use gibberellins to force plants to produce flowers and to increase the size of fruit.

They can also be activated to produce fruit without pollination, and so make seedless fruit.

Ethene is a plant hormone that causes ripening of fruit.

And commercial fruit growers use ethene to speed up the fruit ripening so that the fruit can be picked unripe, and then ripened at the point that it is ready for sale.

So well done for your work in today's lesson, and we'll see you soon.