Embryology is the study of the development of embryos. By comparing embryological development of different organisms, scientists can identify relationships.
Enzymes play an important role in chemical digestion.
The esophagus is a muscular tube that carries food from the mouth to the stomach through waves of muscular contractions called peristalsis.
The main organs of the human urinary system include two bean-shaped kidneys located at the bottom of the rib cage near the back. Kidneys perform the very important job of removing nitrogen-containing wastes from the blood.
When a pollen grain lands on the sticky stigma, it forms a pollen tube through the thin style to the ovary. Once in the ovary, the pollen tube enters the ovule. Two haploid sperm nuclei then enter the embryo sac.
In most bryophytes, the haploid gametophyte phase is dominant. It's what we commonly recognize. Bryophytes tend to produce separate male and female gametophytes.
When a mature spore is released and lands in a suitable location, it develops into a tiny, heart-shaped haploid gametophyte form called a "prothallus."
Pollen is transferred via the wind or by other means from the male pollen cone to the female seed cone. Of the millions of pollen grains released from sporangia, some land on the scales of female cones near an opening called the "micropyle."
Female cones, seen here, possess ovules that produce egg cells.
Gametophytes are quite small in angiosperms and develop in the flower of the sporophyte plant. Female eggs form in ovules inside the ovary of the flower.
In the male reproductive part of the flower, haploid spores called "microspores" are produced in a structure called the "anther." The microspores consist of two-celled male gametophytes that together make up a pollen grain.
The fundamental filtering units in the kidneys are nephrons. Each kidney contains over one million nephrons. Most of the fluid is returned or reabsorbed by the bloodstream along with other substances needed by the body.
The small intestine is a hollow tube that is only about 2.5 centimeters in diameter, but it stretches about 7 meters in length. The chemical digestion of carbohydrates and proteins is completed in the small intestine.
One of the most important ways the body excretes wastes is via specialized structures in the urinary system.
Urine passes out the kidneys to the bladder through small tubes called ureters. From time to time urine is emptied from the bladder through the urethra.
Food travels through the esophagus via rhythmic muscular contractions referred to as peristalsis.
Nutrients are absorbed into tiny blood vessels found inside villi. Blood then carries nutrients throughout the body.
A male sex cell unites with a female sex cell to form a fertilized egg.
Capillaries are microscopic vessels where food and gases are exchanged with cells of the body.
When the coronary arteries, which supply blood to the heart, become clogged with fat, it is more difficult for blood to nourish heart muscles. When blood flow to the heart is cut off or greatly reduced, a heart attack might occur, damaging the heart.