Growth and development of animals
When the sperm fertilizes the egg, a zygote is formed. The zygote undergoes multiple cell division (the number of cells grows but the cells get smaller) in mitosis which ends in formation of an embryo. So there are a lot of small cells but the size of the embryo doesn’t change. This stage is called cleavage. The result of cleavage is formation of a blastula: a ball of cells with a cavity.
The next stage is gastrulation. During this stage the embryo forms the second layer of cells. Now the embryo consists of two layers of cells: outer layer (ectoderm) and inner layer (endoderm). The third layer, mesoderm, forms later.
The neural plate is the next stage of embryo formation. At this stage the organs begin to form. Ectoderm develops into the nerve cord (and then – into the brain and the spinal cord). Ectoderm also develops into epidermis, sight organs and hearing organs. Endoderm develops into intestines, digestive organs, lungs. Mesoderm develops into skeleton, muscles, cardio-vascular system. In the end of this stage the organs of the embryo can be vaguely differentiated. This is the final stage of embryonic development.
When the organism is born, it can look like an adult parent-organism (direct development) and it can differ from the adult organism – larva (indirect development). When the offspring doesn’t look like its parent, the two organisms cannot compete: the butterfly eats nectar and the caterpillars – plant leaves; the frogs eat insects and the tadpoles – plants.
A sperm – сперматозоид
To fertilize – оплодотворять
An egg – яйцеклетка
A zygote – зигота
To undergo multiple cell division – подвергаться множественному делению
Mitosis – митоз
An embryo – зародыш
A size – размер
Cleavage – деление клеток
A blastula – бластула
A cavity – полость
A stage – стадия
Gastrulation – гаструла
A layer – слой
Outer – внешний
Inner – внутренний
Ectoderm – эктодерма
Endoderm – энтодерма
Mesoderm – мезодерма
A neural plate – нейрула
Formation – формирование
To develop into – развиваться во что-то
A nerve cord – нервная трубка
Brain – головной мозг
Spinal cord – спинной мозг
Epidermis – кожа
Sight organs – органы зрения
Hearing organs – органы слуха
Intestines – кишечник
Digestive organs – органы пищеварения
Lungs – легкие
Muscles – мышцы
Cardio-vascular system – сердечно-сосудистая система
Vaguely – едва
To be differentiated – быть различимым
Final – конечный
To be born – родиться
To look like – быть похожим на
Direct development – прямое развитие
Indirect development – непрямое развитие
To differ from – отличаться от
Adult organism – взрослый организм
Larva – личинка
An offspring – отпрыск
To compete – соревноваться
A caterpillar – гусеница
A tadpole – головастик