AP BIOLOGY

Detailed explanation-1: -Energy is required to do useful work, such as the transport of metabolites across membranes, the driving of anabolic reactions and to cause movements in organisms. Cell respiration involves the oxidation and reduction of electron carriers.

Detailed explanation-2: -In active transport, substances move against a concentration gradient across a cell membrane. Hence energy is required. The energy available in the body in the form of ATP is used to move this substance across the cell membrane.

Detailed explanation-3: -Osmosis is a special type of diffusion, namely the diffusion of water across a semipermeable membrane. Water readily crosses a membrane down its potential gradient from high to low potential (Fig. 19.3 ) [4]. Osmotic pressure is the force required to prevent water movement across the semipermeable membrane.

Detailed explanation-4: -Enzymes are crucial to metabolism and allow the fine regulation of metabolic pathways to maintain a constant set of conditions in response to changes in the cell’s environment, a process known as homeostasis.

Detailed explanation-5: -Anabolic pathways build complex molecules from simpler ones and typically need an input of energy. Building glucose from carbon dioxide is one example. Other examples include the synthesis of proteins from amino acids, or of DNA strands from nucleic acid building blocks (nucleotides).