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Chapter 25 -- Part 1: Introduction
Three and a half billion years ago, a common ancestral cell is believed to have descended from a ll organisms.
According to the theory of endosymbiosis, eukaryotic cells emerged when the free-living prokaryotes took up permanent residence inside other larger cells about one and a half billion years ago.
The rapid evolution of multicelled organisms can be traced back to the advent of the more complex cell with internal membranes.
According to modern cell theory, all organisms are composed of cells.
Human red blood cells have a diameter of only 8 um, but most animal and plant cells have diameters between 10 and 100 um.
They are all enclosed by a protective barrier.
Subcellular components are suspended in a semifluid substance called cytosol.
All cells contain ribosomes and genetic material.
There are two types of cells.
The cells that are prokaryotes are simple.
bacteria are prokaryotic cells Instead of a nucleus, they have a non-membrane bound region where the chromosomes are located.
Eukaryotic cells have a nucleus.
Complex chemical reactions can be carried out efficiently in separate regions of a cell with the help of the organelles and internal membranes.
The cells of the human body are called eukaryotic cells.
Understand the difference between prokaryotic and eukaryotic cells.
Function dictates form and vice versa is a major theme in biology.
One would expect that all cells look different.
The nerve cell is long and spindly.
The cells that store fat are rounded.
The tough peach pit is made of cells that look like building blocks.
Function and form go together.
As you read the book, look for examples.
The cells are all tiny.
The surface area of the cell should be able to accommodate the needs of the metabolism based on the volume of the cytoplasm.
The two "cells" are compared.
6 to 1 is the ratio of the surface area of the cell to the cube's total volume.
The surface area to volume of the 5mm cube is less than 1 to 1.
The smaller cell will be more efficient at supplying needed materials and removing waste than the larger cell.
Multicelled organisms consist of millions of tiny cells carrying out specialized functions rather than one big cell.
As a cell grows and the volume of the cytoplasm becomes too great for the area of the cell membrane, a pathway is triggered and the cell divides in two.
It is possible to use surface area-to-volume ratios to predict which cell will eliminate waste.
Cell walls in plant cells are unique to each cell type and are one of the unique parts of the eukaryotic cell.
The human body has approximately two hundred different cell types, each with a different function and a different form.
Different cell types have different looks, but they all have the same thing.
The nucleus of a non-dividing cell contains a prominent nucleoli, where ribosomal RNA is made.
There are large and small ribosomes assembled there.
The rRNA is made in the nucleolus.
Nucleoli are a tangle of unfinished and incomplete ribosomal structures.
There are ribosomes that are made of proteins.
They are not considered to be part of the body.
Ribosomes can be found in the cytosol or in the reticulum.
ribosomes attached to the reticulum are meant for export out of the cell, while free ribosomes are meant for the cell's own use.
Pancreatic cells contain millions of ribosomes and produce huge amounts of hormones.
Both plant and animal cells have peroxisomes.
They contain catalase, which converts hydrogen peroxide into water with the release of oxygen atoms.
They remove alcohol from the cells of the liver.
The cell's metabolism is regulated by the endomembrane system.
The nuclear envelope, Golgi apparatus, lysosomes, vesicles, and vacuoles are included.
Cell processes can be aided by increasing surface area and decreasing competing interactions.
The nucleus has chromosomes that are wrapped around a network of genes.
The nucleus is surrounded by a nuclear envelope that separates it from the rest of the body.
The nuclear envelope has pores to allow for the transport of large Molecules, like mRNA, which are too large to diffuse directly through the envelope.
The ER is a membranous system of channels and sacs in the nucleus of a cell.
The ER is studded with ribosomes.
The Golgi apparatus consists of flattened membranous sacs, called cisternae, stacked next to one another.
The two sides of a Golgi stack are referred to as a cis face and trans face.
The material from the ER is carried to the cis face where it is processed and packaged into vesicles.
They are shipped out from the trans face to different parts of the cell.
A cell may have many Golgi stacks.
There are sacs of hydrolytic enzymes in lysosomes.
They are the main site of digestion.
The lysosome helps the cell to keep renewing itself by breaking down and recycling cell parts.
A key part of the development of multicelled organisms is the destruction of cells by their own hydrolytic enzymes.
Plants don't usually have lysosomes in them.
The site of cellular respiration is the mitochondria.
A very active cell could have as many as 2500 mitochondria.
The cristae is a series of cells in theMitochondria.
Mitochondria have their own genetic material.
In order to compensate for one another's defects, the Mitochondria constantly divide and fuse with each other.
This is needed for normal mitochondrial function.
The endosymbiotic theory is supported by the fact that mitochondria have their own genes.
The theory says that prokaryotic cells were once free-living and that they took up permanent residence inside larger prokaryotic cells billions of years ago.
There are structures used for storage.
They are derived from the ER and Golgi apparatus.
Plants have a single large central vacuole.
Contractile vacuoles are used to pump out excess water.
Food vacuoles are formed by foreign material.
Chloroplasts have a green color that absorbs light energy and makes sugar.
They are found in plants.
They have a double outer and inner system.
According to the theory of endosymbiosis, small prokaryotic cells used to be covered by larger prokaryotic cells.
The engulfed cell became a permanent resident and the two became one entity.
A major piece of evidence for this theory is that the chloroplasts have their own genetic material.
The cell's cytoskeleton is made of a complex mesh of proteins.
There are several important roles for the cytoskeleton.
It keeps the cell's shape.
The position of the cell's organelles is controlled by anchoring them.
It is involved with the flow of the cytoplasm.
The cell is anchored by interacting with the elements.
Microtubules and microfilaments are included in the cytoskeleton.
There are hollow tubes made of the tubulin that make up the cilia, flagella, and spindle fibers.
9 pairs of microtubules are organized around 2 singlet microtubules, which move cells from one place to another.
There are 9 triplets with no microtubules in the center of them.
When present in prokaryotes, flagella are not made of microtubules.
Microfilaments are used to support the shape of the cell.
The 9 + 2 configuration is used by Cilia and flagella.
Centrioles, centrosomes, or microtubule organizing centers are nonmembranous structures.
They organize the fibers and give rise to the apparatus needed for cell division.
Two centrioles oriented at right angles to each other make up one centrosome.
The plant cells do not have centrosomes.
The centrosome is synonymous with the MTOC in animal cells.
The cell wall is not found in animal cells.
Cell walls are made of cellulose.
The cell walls are made of chitin.
Prokaryotes have other polysaccharides and complex polymers.
The primary cell wall is outside.
There is a second cell wall underneath the primary cell wall.
A thin gluey layer is formed between the two new cells when a plant cell splits.
The steady traffic that enters and leaves the cell is regulated by the cell or plasma membrane.
The fluid mosaic model was described by Singer in 1972 and he is famous for it.
There is a bilayer oflipids with a mixture ofproteins dispersed throughout the layers.
Alipid is an amphipathic, meaning it has both a hydrophilic and a hydrophobic region.
hydrocarbons, carbon dioxide, and oxygen are not polar and can be dissolved in the bilayer without the need of a membranes.
The flow of ion and polar molecule is impeded by the interior of the membrane.
It is not easy for polar molecules to pass through the inner layer.
Water is a very small polar molecule.
There are nonpolar regions that span the interior of the Membrane.
The surface of the membrane is bound to the peripheral proteins.
Cholesterol is found in the interior of the bilayer.
The average membrane is composed of 40 percent lipids and 60 percent proteins.
The Phospholipids move quickly.
Some are kept in place by being attached to the cytoskeleton.
The glycoproteins and the glycolipids are found on the outside of the cell.
Both structures can be used to distinguish one cell type from another.
The surface of red blood cells are home to a number of blood types.
Explain how the structure relates to its function.
There is a wide range of functions provided by thetrypsinogen.
Transport consists of channels, pumps, carriers, and electron transport chains.
The adenylate cyclase is one of the membranes boundidases.
The binding sites on the proteins are similar to hormones.
The message is sent to the inside of the cell.
The identification flags that are recognized by other cells are served by some glycoproteins.
Desmosomes, gap junctions, and tight junctions are examples.
This helps maintain cell shape and the location of certain proteins.
Substances are moved into and out of a cell.
Transport can be active or passive.
Energy is required for active transport.
No energy is required for passive transport.
Facilitated diffusion doesn't use the drug.
When equilibrium is reached, a region of high concentration is replaced by a region of low concentration.
There are some examples of passive transport.
Simple and facilitation are the two types of diffusion.
Simple diffusion doesn't involve any of the channels.
Simple diffusion can be found in the glomerulus of the human kidneys, where solutes dissolved in the blood diffuse into a capsule.
Facilitated diffusion requires a channel that will speed up the transport of substances across the membranes.
In the passage of an impulse along an axon, voltage gated ion channels are important.
Simple and facilitation do not require energy.
Countercurrent exchange is a special case of simple diffusion in which fluids flow in opposite directions.
One example of countercurrent exchange can be seen in fish.
Water flows over the gills in the opposite direction as blood flows toward the head.
The process maximizes the dispersal of respiratory gases and waste between the water and fish.
Here are some words to help you understand passive transport.
Scientists look at the movement of water in terms of water potential.
solute concentration and pressure are two factors that affect water potential.
Adding solutes lowers the water potential to a value less than zero.
The cell has a negative water potential.
The higher the water potential, the easier it will be for water to move across the membrane.
A sketch of two containers is shown in figure 3.12.
There is a solution A and a solution B.
The water moves toward the hypertonic area.
The cell is in an isotonic solution.
There is no net change in the size of the cell as water diffuses in and out.
Understand how they affect living cells and design an experiment to demonstrate that.
There is a lab on this page.
The cell is in a solution.
The beaker has less solute in it than the cell.
The water will cause the cell to swell or burst.
The cell wall will prevent the cell from bursting.
The cell will swell or become turgid.
Plants like celery are kept crisp by this turgid pressure.
If a plant loses too much water, it will lose its turgor pressure.
The cell is in a solution.
The beaker has more solute in it than the cell.
Water will flow out of the cell if there is high concentration of water and low concentration of water.
The cell shrinks due to plasmolysis.
Up to 3 billion water molecule per second can be achieved by the use of aquaporins in certain cells.
The rate at which water diffuses down its gradient is what these channels do not affect.
It is possible that aquaporins can function as gated channels that open and close in response to certain variables.
The action of aquaporins may be to blame for the sudden change in a cell.
While aquaporins facilitate the rapid passage of H 2 O across the membranes, they won't carry hydronium ion.
The hydronium ion is charged and the water molecule is not.
Many channels are very specific.
The movement ofmolecules against a gradient requires energy and is called active transport.
There are a lot of examples of active transport.
Particles are carried by active transport by pumps or carriers.
The pump moves Na + and K + ion against a gradient, pumping two K + ion for every three Na + ion.
The Na-K pump is used in animals.
Homeostasis can be achieved by the constant movement of molecules.
They store energy that can be used for cellular work.
The production of ATP in the cristae membranes is an important example.
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