Plant Growth and Development

This one around growth and development of plants so plants are able to grow throughout their lifetime through the presence of undifferentiated tissues called meristems now when we look at this word undifferentiated we are reminded of their own stem cells within our bodies they’re not nerve cells they’re not muscle cells they’re not skin cells that type of thing they’re undifferentiated and if we remember from the last screencast.

We talked about that in most cells within a planner totipotent which means that they have the ability to take on the characteristics of other differentiated cells within that plant so if it needs to be a root it can be a root if it needs to be a stem it can be a stem that type of thing the tumor stems that we are going to concern ourselves with are apical and lateral meristems apical meristems are going to give the plant primary growth.

They are going to cause a the stem of the root to grow longer they’re going to give it length and they’re located at the tips and lateral meristems are going to add secondary growth and they’re going to crop they’re going to cause that plant to increase in girth or width so listen if I if I have a tree.

I’m an out of ground now here’s what I do I’m gonna put a nail right there and then I’m going to wait 25 years in 25 years I’m gonna get all kinds of growth hopefully this thing is going to grow it’s going to flourish now we ask ourselves where is that nail after 25 years apical meristems where are those apical meristems dirt the tips right so where’s the nail it’s right where we left it right there it’s not up here somewhere right because that’s because the growth isn’t occurring from down here awesome all right well.

Now let’s talk about lateral meristems because if this is like an oak tree or something like that we get that secondary growth that male might that nail might be inside that bark it might be inside that secondary xylem have you ever seen those things basically they sell them to put on your tree like nail them to your tree they’re like little eyes and a mouth and after a few years that secondary growth will actually grow over those eyes like around that mouth and it actually looks like hey that’s a face on my tree.

So, let’s talk about reproduction in angiosperms specifically right so this is the anatomy of a flower look it’s just it’s prior knowledge but we’re going to do a quick brief review here this idealized flower has male structures called the stamen which is composed of both an anther and a filament the anther is the site of pollen production so what do you think this filament is doing we look at look at the evolutionary advantage.

That filament gives you’ve got a pollinator that’s coming along and landing on this flower right well if that anther is way down there bye-bye the receptacle down here nestled next to the ovary the chance of that bee or hummingbird or whatever getting into that pollen on it to then go and pollinate another flower it’s kind of low but look at that filament does it just kind of presents that an throughout right let’s look at the female part of the plan called the carpals sometimes called the pistil bist il a you have the stigma the style.

So, do you remember alternation of generations this is what it looks like inside of an angiosperm this’ll live cells an angiosperm it’s a great overview of the reproductive process so again just to remind you you do not have to memorize a any particular life cycle ie., alternation generation surveying the four different types of plants but just to understand the basic concept of this alternation between a ployed and diploid and what we see here is that fertilization is going to occur with a male gamete fertilize it with the female gamete to form the plant embryo now at that point this zygote is now diploid right our sperm and egg were haploid now the next three slides are going to cover a concept called double fertilization.

This is double fertilization is unique to angiosperms though the details us of particular reproductive cycles of plants and animals are no longer specifically covered on the AP Biology exam double fertilization it’s so crucial to the evolutionary success of angiosperms that we must visit it and discuss it for the exam so here we have the carpel or the pistil  you have the you have the stigma style and the ovary and we can see polar nuclei in here and we can see the egg.

If the the pollen tube if if this pollen grain basically germinates it’s going to grow this it’s going to start growing mitotically down it’s going to grow this pollen tube and i want you to pay special attention to these two sperm that are coming down with that the pollen tube is going to discharge the two sperm into this female gametophyte called the embryo sac within this ovule and basically one sperm is going to fertilize the egg which forms the zygote the other sperm combines with the two polar nuclei of the embryo sacs large central cell forming a triploid cell.

This is going to develop into nutritive tissue called endosperm now these two events comprise what we call double fertilization you fertilize the zygote and you’ve combined that that other sperm with the two polar nuclei making endosperm this is double fertilization and it is very unique to angiosperms now we think of endosperm it is in a very important component of our human diet worldwidefor instance let’s take wheat for an example the endosperm is out of week.

It’s the endosperm is selectively taken out in the process in this food we call it white flourthe embryo itself which we call germ the seed coat which we call brand are removed now if you root now if you keep the embryo and the seed coat the germ and the bran you keep those in there now we call that whole wheat right some other examples of endosperm would be the milk or the meat quote-unquote in a coconut also the nutritive tissue inside of corn kernels that’s endosperm as well.

These pollinators are flower specific these pollinators will only pollinate certain types of plants which have certain types of flowers the flowers are going to evolve along with these pollinators just for some examples butterflies see yellow thus the flowers a pollinator yellow moths are out most frequently at night so therefore they pollinate white flowers that are fragrant be CLO blue and UV light the flowers they pollinate are yellow or blue and you can see that UV radiation hummingbirds need a lot of sugar.

They see red they pollinate flowers that are red and usually have these significant nectar reserves bats and possums are nocturnal and pollinate flowers that are fragrant and attract insects the pollinators and flowers have co-evolved together let’s take a example of this relationship for example the California Buckeye tree is pollinated only by native California honeybees that are immune to the neurotoxin found in the pollen other honeybees are sensitive to this pollen.

So, in so on so only these California honeybees are immunised neurotoxin so they’re able to actually pollinate that tree the flowers on that tree some orchids actually resemble insects so male insects will come along they’ll actually try to mate with these orchids in an effect they are actually involved in the pollination of these flowers right so here’s let’s look at the structure for mature seed you see a seed coat you see other structures within that basically associated with endosperm the different parts of the embryo your first seed leaf your first root that type of thing a seed consists of a dormant plant embryo.

It’s surrounded by its food supply the cotyledons the endosperm or both the seed is surrounded by this hard protective seed coat dormancy describes appeared when the embryo within a seed stops growing and its metabolism nearly ceases this is sending any adaptation for tough times whether that be drought or freezing winters that type of thing certain environmental conditions can trigger the seed to break this dormancy now it’s important the timing of seed germination.

It’s reliance on both temperature and water are specifically tested on the AP biology exam there’s two types of germination germination begins with imbibition the uptake of water by a dry seed rupturing of the seed coat triggers metabolic changes that allow the plant embryo to resume growth now the timing of seed germination and its reliance on temperature and water again just to point out.

These are specifically tested on the AP biology exam low water potential of the seed triggers this imbibition in common in a here we see a common garden beans we see some common garden beans the straightening of a hook on the on the hypocotyl pull the cotyledon from the soil in maize and other grasses that we see down here and be the chute grows straight up through the tube of the coleoptile.

Breaking dormancy is a phenomenon attributed to enzymes and hormones within these seeds the essential seed related anatomy terms are cotyledon endosperm and radical so do dry seeds respire yes well unless they’ve been suffocated in a plastic bag or become completely dehydrated finally let’s just look at some adaptations for seed dispersal how do these seeds get out into how are they propagated out away from the mother plant right and again you wouldn’t need to memorize all of these but be able to discuss one or a few right.

So, first we see over here some are wind like a dispersed like milkweed or a dandelion or maple you’ve probably seen these little helicopter guys coming down to the ground right maybe they’re propagated by animals we have begger ticks and sand birds and blackberry these things have some some spines on there and they’re going to be able to just stick to animals that are walking by right they’re going to basically go disperse that somewhere else even by water you see a Lotus cattail even a coconut well.

We actually what most people think is the coconut is actually the seed right and so that’s within this big hairy fruit and that’s going to be able to just bob up and down in the waves until it lands on some ground and then be able to to grow from there some flowers just burst open like a violet or witch hazel or jewel weed right they just burst open in the seeds go flying right some of them we put these seeds in these of these fruits that humans like beans and wheat all right and cherries these things have seeds unless.

We’ve genetically taken them out obviously but but you know we can disperse that we can do that again please make sure that you go through this and this screencast and all screencast as many times as you need to stop take some notes ask some questions ask your teacher and I really do believe that this is going to help you with the growth and development of specifically the angiosperms on the AP Biology scene.

Leave a Comment