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Biology AS
OK. So let’s see what these bits do. Of course, this is the best part of biology. Learning
definitions.
Stamen:
the male organ of a flower which produces pollen and usually consists of an
anther and a filament
Anther:
pollen-containing sac of stamen at the summit of the filament
Filament:
part of the stamen which supports the anther
Carpel:
Female reproductive organ of flowering plants, consisting of stigma, style and
ovary. In some plants, one or more carpels unite to form the pistil.
Pistil:
the female organs of a flower made up of all the carpels
Stigma:
part of the female organ of a flower adapted for reception and germination of
pollen
Style:
the elongated portion of the pistil between the ovary and the stigma carrying the
stigma
Ovary:
the basal part of the female organ of a plant in which seeds develop.
Ovule:
structures in ovaries that contain eggs and when fertilized by pollen, develop
into seeds
Receptacle: structure at the base of a flower which attaches the flower style to the stem. The
receptacle will often break down in a fertilized, mature flower to aid in dispersal
of seeds
Sepal:
the sepals are attached to a flower underneath the petals. They protect the flower
before it opens, while it is a bud
Petal:
an often brightly-coloured modified leaf, to attract pollinators.
So let’s play a game…hmm. Not so sure actually. There’s not really enough time so we may
just have to let this go this time. We’ll try at the end of the lesson and see how it goes.
What is pollination?
To transfer pollen from the anther of a stamen (male) to the stigma of a pistil (female),
resulting in fertilisation. This can occur either on a single plant (self-pollination) or between
different plants. Insect pollination and wind pollination are two examples of natural
pollination.
If you are finding it difficult to remember which parts of the flower are male and which are
female, then just remember that it’s the men that do all the work: their pollen moves to the
woman’s part that just sits at home with the eggs….ok?
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A joke about men… (seeing as you thought it was a bit unfair to say that about women…)
When Dan found out he was going to inherit a fortune when his sickly father died, he decided
he needed a woman to enjoy it with. So one evening he went to a singles bar where he spotted
the most beautiful woman he had ever seen. Her natural beauty took his breath away “I may
look like just an ordinary man,” he said as he walked up to her, “but in just a week or two, my
father will die, and I'll inherit 20 million pounds.”
Impressed, the woman went home with him that evening and, three days later, she became his
stepmother.
As you can see, intelligence plays an important role in life. It’s true of plants too. Plants are
smart. That’s the only way that they can get pollination to work.
Pollination adaptations
Flowers need to be pollinated. Pollination is the process of moving the pollen grain from the
anther of a stamen to the stigma of a carpel. There are a few flowers that can self-pollinate all
on their own, but this limits them to inbreeding. Most species rely upon some kind of
pollination vector to accomplish pollination. The vector can be any agent that can move pollen
from anther to stigma.
Pollination by animals: adaptations
What colourful petals you have…
Some species use a color pattern known as a "bull's eye" to mark their position
in the environment...to stand out against a background of green foliage.
Obviously not too many animal-pollinated flowers
are leaf-green!
-
Not all animals see all colours
-
Bee vision does not include red, but it does extend
into the ultraviolet. In other words, bees see colors
that are invisible to us
-
Some plants not only look good to us, but also look
good in the colours that the pollenators can see
Smells nice…
Some pollinators are more olfactory (smelly) than visual, and of course, some
use both senses.
-
Flowers have evolved fragrances and this results in efficient pollinator
attraction. Again, different animals have different sensibilities and sensitivities
to fragrances.
-
Bees are attracted to certain scents, particularly those we might describe as
sweet or spicy
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Rewarding the pollinator
Now this makes sense…the only reason we do anything….to be rewarded!
Once the pollinator has made the first landing, the flower needs to reward the
animal so that it will perceive the reward as a result of its visit. Its intelligence
will then allow it to decide to visit similar flowers nearby to obtain additional
rewards
-
Nectar is basically what comes out from the phloem. It is mailny sugar and very
high energy food
-
Pollen is actually also a source of protein, vitamins and minerals and as plants
often make excess pollen, the pollinators can use this too
Wind Pollination
Well, there’s not a lot to say really. It’s straight forward: instead of animals…wind is used!
These flowers often don’t have colourful petals or nectar. Instead they rely on luck and hope
that their pollen is transferred to the right place on another plant.
Plants that do this often have longer stamens so that they are more likely to have pollen hit
them.
Cross pollination (when pollen goes from one plant to another (rather than being in the same
plant)) obviously has its advantages: the main one being variety in the offspring.
These words are mentioned in your syllabus…Allah knows why…..but anyway:
Protandry: Male organs develop before female organs so that self pollination can’t occur
Protogyny: Female organs deveolp before male organs so that self pollination can’t occur
Dioecious: Producing male and female flowers on separate plants (as with wind pollination)
Syllabus checklist…
2B.4 Sexual reproduction
know that offspring result from the fusion of gametes, forming a zygote;
understand that this fusion of gametes leads to genetic variation in offspring;
recall that gamete formation involves a reduction division (meiosis) and
understand its significance as the division of a diploid nucleus to give haploid
nuclei;
understand the behaviour of chromosomes during the first and second divisions
of meiosis, including chiasmata formation (names and details of stages of
prophase are not required);
understand that haploid and diploid phases occur in the lifecycles of organisms.
Reproduction in flowering plants
describe the structure and functions of the principal parts of an insect-pollinated
dicotyledonous flower and a grass;
describe pollination and the events leading to fertilisation;
understand the adaptations related to insect and wind pollination;
describe and appreciate the significance of the mechanisms for ensuring crosspollination; protandry, protogyny and dioecious plants.
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Biology AS
Right….enough of that botany stuff. Let’s get on to the real stuff: HUMAN reproduction.
I think I’ll let you decide which one is male and which is female................
In males, the sperm is created in the testes and travels up past the epididymis and through the
vas deferens. Various fluids are added to it as it passes through the tubes out of the penis.
In the female, the egg (ovum) is created in the ovary. Many many eggs are created from birth,
but only one every month (normally) is released from the ovary to the fallopian tube. The
ovum is generally fertilised here as the sperm, which is deposited in the vagina, travels up
through the uterus to the fallopian tube.
So what we will do now is look at the beginnings of life. That’s right. The beginning of life.
Imagine that. And you said biology was useless. Pfft…what do you know!
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Spermatogenesis
-
this is the process in which a male
spermatogonium develops into a mature
spermatozoon (sperm)
-
obviously you know that spermatozoon is
the male gamete
-
certain conditions are needed for this to
occur (e.g. presence of testosterone)
-
it is essential for sexual reproduction
(obviously…no sperm = no fertilisation =
no cute baby)
-
it starts at puberty and continues until death
-
as you can see from the diagram there are
different stages and the final product has 23
chromosomes (i.e. is haploid)
-
it takes place within the male reproductive
system starting from the testes to the
epididymis where the gametes are stored
until ejaculation
-
strangely enough, oogenesis happens before
the girl is even born!
-
these then form the primary oocyte a few
months after birth
-
these start to divide by meiosis but are
stopped in prophase 1 until puberty
-
at puberty, a few oocytes begin to develop,
although only 1 or 2 are released
-
there are various layers covering the oocyte
including the zona pellucida
-
the oocyte undergoes meiosis forming what is
called a second polar body
-
this doesn’t actually do anything…
-
but the first polar body then begins the second
meiosis cycle and is stopped at metaphase 2:
this is when it is released from the ovary
-
it only completes this meiosis if it is fertilised
by a sperm
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Biology AS
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