The two important branches of biology are botany and zoology.

Mammal embryos don't require a large yolk becaues they are nourished directly by the mothers body. In contrast, birds, reptiles, and other (mostly) egg layers, need a large yolk because the yolk must nourish the embryo all the way through development.

No, not all animals start life as an embryo.

In protostome ("first mouth") the blastopore, or the first opening formed becomes the mouth. In deuterostomes ("second mouth"), the blastopore forms the anus and the mouth develops from a second opening.

No. Many, in fact most eggs are not fertilized and are therefore not viable.

Baby koalas (joeys) are born after a gestation period of just 35 days. After birth, the tiny, blind, hairless, bean-sized koala embryo emerges and moves into its mother's pouch, purely by instinct. At this stage it weighs about half a gram. Once in the mother's pouch, it then latches onto a teat, which swells in its mouth, securing it firmly so it does not fall out of the pouch. The koala baby, called a joey, feeds only on mothers' milk for 6-7 months.

To make the transition from mothers' milk to eucalyptus leaves, at about 6-7 months the joey begins to feed on "pap", which is actually a special form of the mother's droppings through which she can pass onto her joey the micro organisms which allow for digestion of eucalyptus leaves. No other animal lives solely on gum leaves, and special proteins are needed to digest them. One of the reasons the koala has a backward-opening pouch is so that the joey can stick its head out and feed on this pap which comes from the mother's own digestive system.

When the joey grows too large to fit in its mother's pouch, it still feeds a bit on mother's milk, lying on her stomach to feed, and spending the rest of its time firmly attached to her back. It only leaves "home" when the next breeding season starts.

Yes, certainly. Many chemicals can cross the placenta. Obvious examples are alcohol and drugs like thalidomide, as well as things like carbon monoxide which impair the proper functioning of blood.

• 
• 2 more answers

It does actually become a body cavity, it becomes the digestive tract; the tube that passes through the body from mouth to anus.

It can be a good indication because mutations affecting embryos are especially detrimental, and so such mutations accumulate less over time.

$5000

• 
• 2 more answers

because their embryos are convinient to study

- each female have millions of eggs that can be fertilized in vitro

- embryos at 48h of development forms a small larvae with all major organs formed : nerve cells, guts, mesodermal squeletton, imune cells etc ...

This is a great advantage, lots of experiments can be done in a short time

- synchronous development : each egg fertlised at a given time and at a given temperature will develop at the very same rate, so lots and lots of camprable embryos can be observed in each experiment (not the same with mouse)

- they are transparent thus easyly observable under a microscope, well suited for all forms of stainings

- Scientists have tools to perform loss and gain of function (shut down or overexpress a specific gene during development)

- Genome of an American specie (S Purpuratus)is fully sequenced, other species will soon have their genome sequenced as well

- They are non chordate deuterostomes. This makes urchins in an evolutionary point of view much closer cousins to human than drosophila (fly) which is as well extensively studied in embryology - roughly : results found in sea urchin may be more likely to reflect a situation found in vertebrates than those found in drosophila

etc etc ...

one major drawback of sea urchins is that its long life cycle (env 2 years) cannot permit the generation of mutant strains (no genetic tools like in mouse zebrafish or drosophila)

An ecosystem is a natural system consisting of all plants, animals and microorganisms, which function with all the physical factors of the environment.

The term ecosystem was coined in 1930 by Roy Clapham, to denote the physical and biological components of an environment considered in relation to each other as a unit. British ecologist Arthur Tansley later refined the term, describing it as the interactive system established between biocoenosis (a group of living creatures) and their biotope (the environment in which they live).

Pancreas

Balut

After 8 weeks

Hopefully it implants to the uterine lining and grows into a fetus

Epicotyl

Gastrulation

A type of egg is composed of a protective shell and membranes that surround the developing embryo is

an egg

The first organ to develop in the embryo is the heart. In a fetus, there is a brain, but it isn't fully developed and can't understand signals from the nervous system. Therefore the first functional organ would be the heart. But the first thing to start developing in a fetus is the nervous system. ( no that isn't an organ )

Many vertebrates retain parts of notochord .

Embryo screening checks an embryo to see if it's carrying any alleles for a genetic disease (e.g. Huntington's disease or cystic fibrosis) so that the parents would know how likely it would be for their offspring to have a genetic disease.

And the reason this is often perceived as a bad thing is due to the choice the would be parents would then make. They would be deciding wether to have a termination because of the genetic disorder. Of course the parents could potentially want to know just to plan the future and an ethically challenging situation would not occur.

biology