The right answer is vein (it contains blood and has valves).
The infra-cardiac veins of small and medium caliber possess this system of fight against gravity. The valves consist of a dense connective tissue, surmounted by endothelial cells, corresponding to a fold of the intima. They allow blood circulation in the sense organ / heart but prevent venous reflux.
Microscopes allowed scientists to observe Prokaryotic cells which make up Bacteria and Archaea. These cells are small and contain no membrane- bound organelles. It allowed them to observe Eukaryotic cells with a nucleus and membrane-bound organelles that perform different life functions.
The thymus gland is the main organ of the lymphatic system. Located in the upper chest region, the primary function of this gland<span> is to promote the development of specific cells of the immune system called T lymphocytes.</span>
Explanation:
Fats are very important classes of food needed by the body. Excess fat is not good for the body.
The following are the reasons fats are essential for the body;
- They provide energy for the body too.
- Fats are good insulators helping to keep the body warm.
- They help the body absorb vitamins because some vitamins are only soluble in fats.
- They help in growing of the cell.
learn more:
Food brainly.com/question/8790597
#learnwithBrainly
Answer:
cellular membranes
Explanation:
Cellular membranes are selectively permeable because they allow only certain molecules to cross into and out of the cell. The phospholipid bilayer is a selectively permeable membrane that surrounds all biological cells. The movement of molecules across the cell membrane bilayer can occur by passive transport (does not require energy) or active transport (requires energy). For example, water molecules pass passively through the cell membrane (passive transport), while other molecules pass through transmembrane proteins against a concentration gradient (active transport).
