Unit 3 Biology HW
One of the cells pictured below is a human brain cell.The other cell is found in human blood. Which cell came from the brain? Explain your answer.
a smaller cell. Because all of these substances must pass through the surface of the cell, a cell that is too large will not have enough surface area to get rid of its wastes and take in what it needs.)
Why are all cells very small? Explain what limits the size of cells.
(All cells are very small because a large cell has a relatively small ratio of surface area to volume. A cell with a large volume also needs more nutrients and produces more wastes than a small cell.
What is endosymbiotic theory? How does it explain the presence of certain organelles in eukaryotic cells?
(Endosymbiotic theory is the theory that some of the organelles of eukaryotic cells, including the mitochondria and plastids (in plant cells), evolved from ancient, free-living prokaryotes that invaded primitive eukaryotic cells. The prokaryotes and eukaryotes had a symbiotic relationship that benefited both of them. Over time, the prokaryotes became permanent "guests" of the eukaryotes as organelles in their cells.
List functions of the cytoplasm and cytoskeleton.
(Functions of the cytoplasm include suspend ing cell organelles, pushing against the plasma membrane to help the cell keep its shape, and providing a site for many of the biochemical reactions of the cell. Functions of the cytoskeleton include helping the cell maintain its shape and holding organelles in place.)
What did Hooke and Leeuwenhoek discover about cells by using a microscope?
(Hooke discovered that cork (a once-living thing) consists of cells. Leeuwenhoek discovered microscopic living things, including tiny animals such as rotifers, blood cells, and bacteria in plaque.)
Compare and contrast simple diffusion and facilitated diffusion. For each type of diffusion, give an example of a molecule that is transported that way.
(Simple diffusion and facilitated diffusion are both types of passive transport. They do not require the input of energy from the cell because substances are moving from an area of higher concentration to an area of lower concentration. Simple diffusion occurs when molecules are very small and hydrophobic, so they do not need help crossing the membrane. Oxygen is an example of a molecule that is transported this way. Facilitated diffusion occurs when molecules are relatively large or hydrophilic, so they need the help of transport proteins to cross the membrane. Glucose is an example of a molecule that is transported this way.
Outline the levels of organization of cells in living things, starting with the simplest level, that of single- celled organisms.
(Starting with single-celled organisms, levels of organization of cells are biofilms, colonies, and multicellular organisms.)
What does the cell theory state? Name the three scientists mainly responsible for developing the cell theory.
(The cell theory states that all organisms are made of one or more cells, all the life functions of organisms occur within cells, and all cells come from already existing cells. The three scientists mainly responsible for developing the cell theory were Schwann, Schleiden ,and Virchow.)
List the four parts that are found in all living cells.
(The four parts that are found in all living cells are the plasma membrane, cytoplasm, ribosomes, and DNA.)
Describe the composition of the plasma membrane.
(The plasma membrane is composed mainly of phospholipids. The phospholipids are arranged in two layers, called a phospholipid bilayer. The hydrophobic(water-hating) tails of the phospholipid molecules are on the interior of the membrane. The hydrophilic (water-loving) heads of the molecules point outwards, toward either the cytoplasm or the fluid that surrounds the cell.)
What is the role of the nucleus of a eukaryotic cell?
(The role of the nucleus of a eukaryotic cell is to control the cell. Because it contains most of the cell's DNA, which is encoded with genetic instructions, the nucleus controls which proteins the cell makes.)
List three structures that are found in plant cells but not in animal cells.
(Three structures that are found in plant cells but not in animal cells are the cell wall, large central vacuole, and organelles called plastids. An example of a plastid is a chloroplast.)
Explain why viruses are not considered to be living.
(Viruses are not considered to be living things because they lack cells and cannot reproduce on their own. Although viruses contain DNA, they do not have a cell membrane, cytoplasm, ribosomes, or other organelles. They also need to use the cells of living organisms in order to make more viruses.)
Create a diagram to show how the cells of multicellular organisms may be organized at different levels, from the level of the cell to the level of the organ system. Give an example of a multicellular organism at each level of organization.
A sponge has the cell level of organization, a jellyfish has the tissue level of organization, a roundworm has the organ level organization, and a human being has the organ-system level organization of the membrane. Hydrophilic molecules can- not cross the plasma membrane (at least not without help) because they are water-loving, like the exterior of the membrane.
Explain how cell transport helps an organism maintain homeostasis.
Cell transport helps an organism maintain homeostasis by keeping things stable inside its cells. For example, cell transport helps keep the concentration of salts, nutrients, and other sub- stances inside cells within the correct range.
Describe the roles of transport proteins in cell transport.
Channel proteins and carrier proteins are two types of transport proteins. Located in the cell membrane, they help molecules and ions pass through the membrane. Channel proteins form pores in the membrane through which hydrophilic molecules and charged ions can pass without making contact with the hydrophobic interior of the membrane. Carrier proteins bind with specific ions or molecules. When they do, they change shape and carry the ions or molecules across the membrane.
What is osmosis? What type of transport is it?
Osmosis is a special type of diffusion. It is the diffusion of water molecules across a membrane, from an area of higher concentration to an area of lower concentration. Therefore, it is a type of passive transport and requires no energy.
Assume a molecule must cross the plasma membrane into a cell. The molecule is a very large protein. How will it be transported into the cell? Explain your answer.
The molecule will be transported into the cell by endocytosis because it is a protein, which is a very large molecule. Vesicle transport is required for very large molecules such as proteins because they are too big to pass through the plasma membrane. Endocytosis is the type of vesicle transport that will move the molecule into the cell.
Explain how the following organelles ensure that a cell has the proteins it needs: nucleus, rough and smooth ER, vesicles, and Golgi apparatus.
The nucleus contains DNA, which is encoded with genetic instructions for proteins. The rough ER is studded with ribosomes, which are organelles where amino acids are assembled and linked together to form proteins. Bits of the membrane of the smooth ER pinch off to form vesicles, which carry proteins to the Golgi apparatus. The Golgi apparatus processes the proteins ,prepares them for use both inside and outside the cell, and sends them on to their destinations (different parts of the cell or the cell membrane for transport out of the cell.
What is the sodium-potassium pump?
The sodium-potassium pump is a type of active transport in which sodium ions are pumped out of the cell and potassium ions are pumped into the cell. Both ions move from areas of lower to higher concentration. ATP provides the energy needed for this "uphill" process, which also involves a carrier protein.
Name two types of vesicle transport. Which type moves substances out of the cell?
Two types of vesicle transport are endocytosis and exocytosis. Exocytosis moves substances out of the cell.
Compare and contrast prokaryotic cells and eukaryotic cells.
• (Both prokaryotic and eukaryotic cells are found in living organisms. Prokaryotic cells do not have a nucleus. Instead, the DNA of a prokaryotic cell is in the cytoplasm. Prokaryotic cells are found in single-celled organisms. Eukaryotic cells have a nucleus that contains most of the cell's DNA. They also have other cell organelles. Eukaryotic cells are found mainly in multicellular organisms.)
