Biology summary
§4.1 reproduction
Animals reproduce in a lot of ways. Reproduction is the process of making
new individuals of the same species.
Asexual reproduction is the reproduction which requires one parent, so an
egg and sperm don’t have to fuse. The offspring are exact copies of the
parent, and therefore, their weaknesses, vulnerabilities etc… are the
same. When the parent has hay fever all offspring have. However, asexual
reproduction allows animals to reproduce quickly, without a mate, and no
time and energy are lost.
Sexual reproduction requires two parents, which need to have different
sex cells to fuse into an individual. The offspring is a mix of the parents,
making it unique.
The sea anemone can reproduce asexual, and sexual. When reproducing
asexually, it splits into two separate individuals. This is called fission,
fission is more likely to happen at a certain size.
Sea anemones can also reproduce sexually. Some species of anemones
are male or female, while other species are both. When an anemone is
female and male it is called a hermaphrodite. It releases sperm and egg
cells in the water, fusing into sea anemone larvae.
§4.2 the human reproductive system
The reproductive organs of males and females grow from the same muscle
tissues. The only difference is the type hormones these tissues are
exposed to when growing. This creates a big difference in structure.
Male
There are male external and internal reproductive organs. The penis and
the scrotum (ballsack) which has the testis (balls) are the male external
reproductive organs. When a boy reaches puberty, the testes begin
producing sperm cells. To make healthy sperm cells, a temperature slighty
lower than 37 C is required. This is why testes hang outside the body,
where it’s several degrees colder. A sperm has a head and a tail, the head
contains hereditary information which will be transmitted to the next
generation. The tail moves the sperm. Sperm develops in the testes in the
seminiferous tubules. Next, sperm travels and is stored temporarily in
the cap-like structure above the testes, the epididymis. Then sperm
travels through the sperm ducts (vasa deferentia). Both testis have an
own sperm duct, which lead to the internal reproductive organs. Sperm
cells need fluid to swim in, and nutrients for energy. They get their
nutrients from the fluid they swim in. The seminal vesticles produce
some fluid, and the prostate gland produces the rest. Sperm cells+the
fluids is called semen. The sperm ducts join in the urethra, a tube inside
the penis transporting semen and urine out of the body. A muscle behind
the bladder prevents urine from entering the urethra when semen exits
, the body. Semen exiting the body is called ejaculation. Blood is pumped
to the erectile tissue to erect so that semen can exit
Female
Most of the reproductive organs are located inside the body. Egg cells
develop in the ovaries. When an egg cell releases it moves to the oviduct.
Here it can be fertilised by a sperm cell. The egg cells are moved by hairs
in the oviduct called cilia, which move the cell to the uterus. Here the
fertilised cell grows into a baby. The bottom opening of the uterus is called
the cervix, this is connected to the vagina. The vagina is also called the
birth canal because a baby travels through it during childbirth. The vulva
is the area where the vagina is open. Next to the vaginal opening there is
another small opening for the urethra where urine passes out. The
sensitive clitoris is above the urethral opening. The vulva is covered by
the inner labia. The inner labia are situated between the outer labia.
Both labia serve as protection.
§4.3 Hormones and puberty
Growth development, glucose levels in the blood the heart rate, and even
the reproductive system can be affected by hormones. Glands produce
chemicals called hormones and are part of the endocrine system. These
hormones affect different target organs, hormones are transported
through the bloodstream. Several hormones control puberty which takes
part around 8-13 years in the reproductive system. The pituitary gland in
the brain triggers the process. More hormones than before are transported
through the blood to the sex organs, the testes and the ovaries will
respond to this by making so-called sex hormones. Sex hormones are
responsible for the development of specific male and female
characteristics. In puberty mental and physical changes occur. In females
a female body shape, menstruation, pregnancy, and the formation of
organs like the breast. In males a male body shape, growth of facial hair,
chest hair, a deeper voice and the growth of male organs like the penis
and testes. Sex hormones also trigger the production of reproductive cells:
egg cells and sperm cells. Egg and sperm cells transfer hereditary
information to the next generation. And affect the brain and behaviour.
The brain is developing, so it replaces old cells with new ones; it reinvents
itself to prepare for adulthood. Teenagers suffer from mood swings;
sometimes it’s a serious threat.
§4.4 The menstrual cycle
Females already have all their egg cells in place when born, but not fully
developed, which starts at puberty and ends at menopause. One egg cell
develops every 28 days. The uterus has to be prepared if the egg cell is
fertilised. The cycle of the development of an egg monthly is called the
menstrual cycle. It prepares a woman for pregnancy. Egg cells contain
hereditary information. From puberty, the female pituitary gland produces
hormones and the egg cells in her ovaries will develop and ripen one by
one. Cells protect and provide an egg cell with nutrients when developing.
Egg cell is now in a follicle, which ruptures so that the egg cell releases
from the ovary to the oviduct. This process is called ovulation. When an
egg cell is released into the oviduct, the uterus lining called the
