Human cells need oxygen for respiration. What system of the body is responsible for transporting an oxygen molecule to different locations throughout the body?

Passive transport refers to the movement of molecules across a biological membrane without the expenditure of cellular energy. This process occurs down the concentration gradient, meaning molecules move from areas of higher concentration to areas of lower concentration until equilibrium is reached. It includes simple diffusion, where small, non-polar molecules like oxygen and carbon dioxide can pass directly through the lipid bilayer of the membrane, as well as facilitated diffusion, where larger or polar molecules move across the membrane with the help of transport proteins, such as channel proteins or carrier proteins. Overall, passive transport is essential for maintaining the balance of molecules within cells and between different cellular compartments.

The cell wall is the part of a plant cell that acts as a barrier and provides support to the cell. It is a rigid, protective structure located outside the cell membrane and is composed primarily of cellulose, a complex carbohydrate. The cell wall gives plant cells their characteristic shape and provides mechanical support, preventing the cell from bursting due to osmotic pressure. It also helps regulate the movement of water and solutes into and out of the cell and protects the cell from pathogens and mechanical damage. In addition to cellulose, the cell wall may contain other polysaccharides, proteins, and lignin, depending on the type of plant cell and its function.

In the life cycle of humans, only sperm and eggs, the gametes, have a haploid number of chromosomes. Haploid cells contain half the number of chromosomes found in diploid cells, which have two sets of chromosomes (one from each parent). During sexual reproduction, haploid gametes from each parent fuse to form a diploid zygote, which then develops into a new organism with a complete set of chromosomes. This process ensures genetic diversity and contributes to the variation observed within populations of sexually reproducing organisms.

Replication, the process of copying DNA to produce identical daughter DNA molecules, takes place in the nucleus of eukaryotic cells. The nucleus contains the cell's genetic material, organized into chromosomes, which consist of long strands of DNA. During replication, the DNA molecule unwinds, and the enzyme DNA polymerase adds complementary nucleotides to each strand, resulting in the formation of two identical DNA molecules. Replication is a crucial process that ensures genetic continuity between generations of cells and is essential for growth, development, and repair of tissues in multicellular organisms.