tasks

Explain why surface area-to-volume ratios are important in affecting a biological system's ability to obtain necessary resources or eliminate waste products.

As an object of a particular shape increases in size, its volume grows proportionately more than its surface area. Thus, the smaller the object, the greater its ratio of surface area to volume. For each square micrometer of the membrane, only so much of a particular substance can cross per second. Rates of chemical exchange with the extracellular environment might be inadequate to maintain a cell with a very large cytoplasm. A sufficiently high ratio of surface area to volume is especially important in cells that exchange a lot of material with their surroundings.

Explain why smaller cells have a more favorable surface area-to-volume ratio for exchange of materials with the environment.

As cells grows its relative surface area ratio decreases and its demand for material resources increases because more cellular structures are necessary to adequately exchange materials and energy with the environment. The surface area must be large enough to efficiently exchange materials. The smaller the cell the more favorable of a surface area to volume ratio for exchange of materials with the environment which is done through diffusion.

Describe the chemical characteristics of membrane proteins, and how this affects their position in the membrane

Integral proteins have hydrophilic regions at the top and bottom of the protein and and a hydrophobic region in the middle. As a result, the integral proteins are embedded in the membrane with the hydrophilic head faces outward and the hydrophobic region is placed between the phospholipids, aligned with the hydrophilic tails. Peripheral proteins don't have a hydrophobic or a hydrophilic region, so they're not embedded in the lipid bilayer.

Describe the components of the cell membrane.

Consists of a lipid bilayer Phospholipids - amphipathic molecules, meaning that it has both a hydrophilic region and a hydrophobic region Integral proteins are able to penetrate the hydrophobic core of the lipid bilayer. Peripheral proteins are not embedded into the lipid bilayer. They are loose appendages. Membrane Proteins: Transport: A protein that is located within the membrane and provides a hydrophilic channel that is selective for a particular solute Some of these proteins help hydrolyze ATP. Enzymatic activity - A protein that acts an enzyme with its active site exposed to substances in the adjacent solution. They carry out steps of a metabolic pathway. Signal transduction - A protein with a binding site of a certain shape that fits a chemical messenger. This messenger sends a signal and changes the shape of the protein. Cell to cell recognition - Glycoproteins can act as identification tags. (Glycolipids + glycoproteins) Intercellular joining - Membrane proteins of adjacent cells can hook together in order to form tight junctions. Channel proteins - has a hydrophilic channel that allow certain molecules or atomic ions to use as a tunnel through the membrane. Carrier proteins - hold onto their passengers and change shape in a way that shuttles them across. Aquaporins - help the passage of water through the membrane. Glycolipids are lipids bonded with carbohydrates while glycoproteins are carbohydrates that are covalently bonded to lipids. Glycoproteins are carbohydrates that are covalently bonded to proteins

Hydrophilic substances (e.g. large molecules and ions), and water.

Hydrophilic substances: Hydrophilic substances diffuse across the membrane via channel proteins or carrier proteins. Channel proteins have a hydrophilic channel that allow hydrophilic substance to travel through the membrane. Carrier proteins hold onto the substances and change shape in a way that shuttles the substance across. Water: Water passes through the membrane with the aid of aquaporins. Aquaporins are integral membrane proteins that have a positively charged center of the channel. Water molecules diffuse down this channel.

Describe the function of the cell walls. Describe the composition and location of plant cell walls.

Only plants contain a cell wall. The cell wall is an outer layer that maintains the cell's shape and protects the cell from mechanical damage; made of cellulose, other polysaccharides, and protein. The cell wall also prevents excessive uptake of water. The cell wall has three main parts, the primary cell wall, the middle lamella, and a secondary cell wall. The primary wall is a relatively thin and flexible wall. The middle lamella is a thin layer of sticky polysaccharides called pectins. The secondary wall has a strong and durable matrix that affords for cell protection and support.

describe passive transport and explain its role in cellular systems.

Passive transport is the diffusion of a substance across a membrane with no energy investment. A substance will diffuse from where it is more concentrated to where it is less concentrated (down its concentration gradient).

Describe the orientation of phospholipids in a cell membrane

Phospholipids have a hydrophilic head that faces outward, and the hydrophobic tails face inward. Phospholipids move in lateral movements.

Compare the structure of prokaryotic and eukaryotic genetic information storage molecules.

Prokaryotic organisms do not have a nucleus in which the DNA is contained. Also, their DNA is contained in a singular circular chromosome and does not contain any histones- it consists solely of DNA. After prokaryotes replicate the chromosome, they divide immediately after. Eukaryotes have a nucleus, have anywhere from 10-50 chromosomes in their somatic cells, and go through a much longer and complex division process to replicate (PMAT).

How is selective permeability related to the fluid mosaic model?

Selective permeability allows the cell membrane to control what substances can enter and exit the cell. The fluid mosaic model is a model that explains how the membrane acts in a fluid structure with various proteins and other large molecules embedded into the bilayer. These proteins, such as channel proteins and carrier proteins, aid in the process of selective permeability.

Describe the movement of the following through the membrane: Small, uncharged polar molecules (e.g. N2), Hydrophilic substances (e.g. large molecules and ions), and water.

Small, uncharged polar molecules: Small, uncharged polar molecules pass through the membrane easily and require no energy input.

What properties do phospholipids give the membrane?

The cell membrane is a bilayer made of up phospholipids and proteins. The phospholipids have a hydrophilic (affinity with water) head and long chains of hydrocarbon tails which are hydrophobic (no affinity with water) thus the hydrophilic heads will face outwards and interact with the aqueous environment and the hydrocarbon tails will form a hydrophobic inner layer thus giving the cell membrane a bilayer structure. Because phospholipids are both hydrophilic and hydrophobic, this structure also results in selective permeability.

What is the role of the cell membrane?

The cell membrane regulates what substances are allowed to enter and exit the cell. It also protects the cell from the external environment, and helps the cell hold its shape.

Explain the physical considerations that determine the upper and lower limits to cell size.

The logistics of carrying out cellular metabolism sets limits on cell size. At the lower limit, the smallest cells are known bacteria called mycoplasmas. They have enough DNA to program metabolism and enough enzymes and other cellular equipment to carry out activities necessary for a cell to sustain itself and reproduce. Metabolic requirements also impose theoretical upper limits on the size that is practical for a single cell.