Eukaryotic cells and prokaryotic cells contain a cytoplasm and ribosomes. Eukaryotic cells have organelles and a nucleus.
Prokaryotic cells were most likely to evolve first because of the simple structure.
Covalent bonding occurs when pairs of electrons are shared by atoms. Atoms will covalently bond with other atoms in order to gain more stability, which is gained by forming a full electron shell. By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability
Answer:
Semi-permeable membrane
Explanation:
In semi-permeable membranes, only some substances can pass through. Sometimes, some can also pass through the channel protein molecules or transport proteins on the cell membrane.
The tiny hollow air sacs in the lungs where gas exchange takes place are the "a. alveoli". These are the "last stop" on the respiratory tree and are responsible for oxygen exchange.
Answer:
1. Aortic semilunar valve
2. Tricuspid valve
3. Mitral valve
4. Pulmonary semilunar valve
5. Mitral Valve
6. Tricuspid valve
Explanation:
The four heart valves of our heart have two main functions. They open to allow blood to pass through them, and close to prevent blood from going back (backflow).
Semilunar valves:
There are two semilunar valves and they have 3 cusps. They open up to areas outside the heart. Their main function is to prevent backflow towards the heart.
a. Aortic semilunar valve is located in between the Aorta and the left ventricle. It opens up to the Aorta where oxygen-rich blood leaves the heart and go towards the other parts of the body. It prevents backflow to the left ventricle.
b. Pulmonary semilunar valve is located in between the right ventricle and the pulmonary artery. It opens up to the pulmonary artery which carries unoxygenated blood towards the lungs. It prevents backflow to the right atrium.
Atrioventricular valves:
They are named as such because they are found in between the atria and the ventricles.
a. Tricuspid valve has three cusps and it is found on the right side of the heart. It is located in between the right atrium and the right ventricle. It prevents backflow to the right atrium.
b. Mitral valve has 2 cusps and that is why it is also known as the bicusip valve. It is located in between the left atrium and the left ventricle. It prevents backflow to the left atrium.
