Biology and Life Sciences - GED Science

Bacteria are prokaryotic organisms and are considered alive. Bacteria can survive and reproduce independent of a host (consider a colony of bacteria cells growing in a Petri dish). Though they do not have membrane-bound organelles, like a nucleus or mitochondria, bacterial cells do have DNA and are still able to produce cellular energy.

This question confuses many properties of viruses with those of bacteria. Viruses are not generally considered alive and require a host cell in order to replicate.

Fungal cell walls can be differentiated from plant and bacterial cell walls in that they are made of the polysaccharide chitin. Plant cell walls use cellulose, and bacteria use peptidoglycan. Amylose is a component of starch.

The plant is only able to use absorbed light during photosynthesis; reflected light cannot be used as energy, as it is simply returned back into the surroundings. Red light will make a plant grow the fastest because it is absorbed. Since green light is reflected, growing a plant in green light will result in very slow growth. The light will effectively bounce off the plant, rather than being absorbed.

Viruses are considered non-living organisms for a variety of reasons. One of the main reasons is that viruses are incapable of creating their own proteins and must hijack host cell ribosomes in order to make them.

Virus structures contain both proteins and nucleic acids, but are unable to replicate their genetic material unless they infect a host cell.

Cellular respiration is composed of many steps used to break down glucose and convert the chemical energy into ATP. Of the four steps described in the answer choices, oxidative phosphorylation via the electron transport chain is the most effective step for producing ATP. The electron transport chain can produce between 32 and 38 ATP from a single glucose molecule.

Glycolysis is the first step of glucose breakdown in cells. This process takes place in the cytosol.

The second step of cellular respiration, the citric acid cycle, takes place in the mitochondrial matrix. The third step, the electron transport chain, takes place on the inner mitochondrial membrane and requires protons to be concentrated within the intermembrane space.

Glycolysis is the first step in cell metabolism. It is responsible for converting glucose (a 6-carbon sugar) into two molecules of pyruvate (a 3-carbon sugar). Glycolysis occurs in the cytoplasm, where the sugar molecules interact directly with enzymes. After pyruvate is created, it is transported to the mitochondria for the remainder of cellular respiration (the citric acid cycle and electron transport chain).

Though plants undergo photosynthesis, they also use cellular respiration. Glycolysis takes place in both animal and plant cells.

Photosynthesis is the process by which plants use the sun's energy to convert water and carbon dioxide into glucose and oxygen .

The equation is the equation for cellular respiration. Cellular respiration happens inside the mitochondria and chloroplast for those cells containing chloroplasts.

The plasma membrane of the cell acts as a semi-permeable barrier, regulating what can enter and exit the cell. Only small, nonpolar molecules are able to cross the membrane via diffusion, without the assistance of protein channels. Larger molecules will be blocked, as will molecules that are charged or polar.

This principle is true for both prokaryotic and eukaryotic cells, and is not affected by the presence of a cell wall. Virtually all organic molecules contain carbon and hydrogen; the presence of these atoms will not affect the molecule's ability to cross the membrane.

A hypertonic solution will have a higher solute concentration than the cell. To reach equilibrium, water must flow so that the concentration fo the solution is equal to the concentration of the cell. In order for this to happen, water must enter the solution, diluting it and reducing the concentration. Water will flow out of the cell and into the solution.

Note that the membrane of the cell will prevent ions from crossing.

Homeostasis describes the resistance of the body to change and serves to reinforce equilibrium. Concentration of ions and water in the blood and regulation of body temperature are examples of homeostatic regulation. These processes must be tightly regulated and maintained in order for the body to operate.

Negative feedback reinforces equilibrium and plays a key role in homeostasis. In a negative feedback system, deviations from equilibrium trigger processes that serve to return the body back to equilibrium. In contrast, a positive feedback system will respond to deviations from equilibrium by enhancing the changes, deviating farther and farther from the equilibrium state.

Hormones can play a key role in maintaining homeostasis, but many other molecules also help return the body to equilibrium.

The plasma membrane of the living cell is made up of a phospholipid bilayer, meaning two opposed sheets of phospholipids with their hydrophilic heads facing outwards, and their hydrophobic tails facing one another. This structure allows the cell to remain fluid in shape while also staying "water tight".

Active transport is the movement of individual small molecules across the plasma membrane against their concentration gradient (from lower concentration to higher concentration). This is usually accomplished by proteins embedded in the membrane which use ATP energy to act as "pumps".

In contrast, osmosis, simple diffusion and facilitated diffusion are all forms of passive transport and do not require additional energy from the cell. These transport methods move with the concentration gradient, rather than against.

Osmosis is the movement of water across a selectively permeable membrane, like the plasma membrane. It flows with its concentration gradient (from high concentration of water to low concentration of water).

A hypotonic solution is a solution that has a lower solute concentration than the fluid in the interior of the cell (the cytoplasm). When the cell is placed in this solution water will flow into the cell via osmosis, causing it to expand and potentially burst.

A hypertonic solution is a solution that has a higher solute concentration than the fluid in the interior of the cell (the cytoplasm). When the cell is placed in this solution water will flow out of the cell via osmosis, causing it to contract.

Exocytosis is the transport of waste materials or secretions from the cells. These molecules are packaged in membrane bound vesicles and are released across the membrane to the outside of the cell.

The "water-loving" hydrophilic heads of phospholipids orient themselves outwards towards the watery cytoplasm inside the cell and interstitial fluid outside the cell. Meanwhile, the "water-fearing" hydrophobic tails of phospholipids orient themselves inwards toward one another.

Interstitial fluid is the substance surrounding living tissue cells, its solute concentration is critical to the maintenance of homeostasis for the cells. Cells may have to spend valuable energy to keep unwanted materials from passing through their semi-permeable membranes in some conditions.