Which of the following statements is true? select all that apply. capillaries have a higher resistance to flow than either arteries or veins. blood travels at a higher velocity in arteries than in veins. the volume of blood flow in the arteries and arterioles is greater than the volume of blood flow through the capillaries. the total cross-sectional area of the capillaries is greater than the total cross-sectional area of the venules and veins. blood pressure is higher in arteries than in veins.

Explanation:

The lumen of arteries is larger than that of arterioles and capillaries. However, even though they have a smaller lumen compared to veins, their walls are thicker to bear the pressure of the blood as it is pumped by the heart to the tissues. Therefore the blood pressure and velocity of blood in arteries (that pump blood away from the heart) is higher than in capillaries and veins. Veins take blood back to the heart from tissues hence this blood is under lower pressure and velocity. This is why veins have valves to prevent the back-flow of blood against gravity.

Due to the large cross-section area of capillaries the blood flow is here is slower hence giving time for blood to linger a bit so there is an exchange of materials between the blood plasma and the interstitial fluids that nourish the cells.

fertilization, pictured in figure 24.23a is the process in which gametes (an egg and sperm) fuse to form a zygote. the egg and sperm each contain one set of chromosomes. to ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. in mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. when a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. in placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in figure 24.23b. the fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. the nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

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wegner's theory did not explain how the continents could move

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