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ลำดับตอนที่ #11 : [[R.S.]]Biology Test::Chapter 7::11.11.08
The Summary of Biology for
Chapter 7 :: Cell Structure and Function
Chapter.7 :: Cell Structure and Function [[Page.168]]
7-1 Life Is Cellular [[Page.169]]
- A common structure that makes up every living thing is the ‘cell’
- In 1665, Robert Hooke used a compound microscope to look at a cork which made up from thousands of tiny, empty chambers. He called them “cells” [[which means tiny room]]
- Around that time, Anton van Leeuwenhoek used a single-lens microscope to observe a tiny living organism in pond water and other things.
- Cells are the basic units of life.
- All the discoveries of cells were summarized in to cell theory, a fundamental concept of biology.
- The cell theory states ::
· All living things are composed of cells.
· Cells are the basic units of structure and function in living things.
· New cells are produced from existing cells.
- Cells can be studied and observed through microscopes.
- Microscope
1. Light microscope = light itself limits the detail of images that can be made
2. Electron microscope = 1000 times more powerful than light micro.
= the samples must be place in a vacuum.
2.1 TEMs [[Transmission electron microscopes]]
· Used to explore cell structures
· Cells and tissues must be cut first into super thin slices
2.2 SEMs [[Scanning electron microscopes]]
· Scan over the surface of a specimen
· Specimens don’t have to be cut
3. Scanning probe microscope = can operate in ordinary air & show samples in solution.
- All cells have two characteristics in common.
· They’re surrounded by a barrier called a cell membrane.
· They contain the molecule that carries biological information – DNA
- Depending on whether they contain a nucleus, cells are divided into two groups.
· The nucleus is a large membrane-enclosed structure that contains the cell’s DNA. It controls many of the cell’s activities.
1. Eukaryotes = cells that contain nuclei
ð Contain a nucleus in which their genetic material is separated from the rest of the cell. [[they’re highly specialized]]
ð Ex. plants, animals, fungi, and protists.
2. Prokaryotes = cells that don’t contain nuclei
ð Have genetic material that is not contained in a nucleus.
ð They grow, reproduce, respond to the environment, etc.
ð Ex. bacteria.
7-2 Eukaryotic Cell Structure [[Page.174]]
- The eukaryotic cell is like a factory ^O^
- Because many of the structures act as if they are specialized organs, they are known as organelles.
- Eukaryotes cell are divided into two major parts :: the nucleus and the cytoplasm.
· The cytoplasm is the portion of the cell outside the nucleus.
[[download pai la ja hen naa]]
= just don’t mind with all the additional parts thingy ok ????=
Parts of Cells
1. Nucleus
- Nickname :: ‘The Control Center’ [[an office/boss in the factory]]
- The nucleus contains nearly all the cell’s DNA and with it the coded instructions for making proteins and other important molecules.
- It is surrounded by a nuclear envelope composed of two membranes.
- The granular material in the nucleus is called chromatin [[consists of DNA bound to protein]]
- When a cell divides, chromatin condenses to form chromosomes [[threadlike structures that contain the genetic info. That passed from one cell to da next]]
- Most nuclei contain a small, dense region known as the nucleolus
· It’s where the assembly of ribosomes begins.
2. Ribosomes
- Nickname :: ‘Small machine’ [[in the factory]]
- Proteins are assembled on ribosomes.
- Ribosomes are small particles of RNA and protein found throughout the cytoplasm. The produce proteins from nucleus’s instructions.
3. Endoplasmic reticulum [[ER]]
- Nickname :: ‘Roads’
- It is the site where lipid components of the cell membrane are assembled, along with proteins and other materials that are exported from the cell.
- Types ::
3.1 Rough ER = involved in the synthesis of proteins [[release + export proteins]]
= ribosomes are found on its surface
3.2 Smooth ER = ribosomes are not found on its surface
= involved the synthesis of membrane lipids and the detoxification of drugs.
4. Golgi apparatus
- Nickname :: ‘The shippers’
- The function of the Golgi apparatus is to modify, sort, and package proteins and other materials from the endoplasmic reticulum for storage in the cell or secretion outside the cell.
5. Lysosomes
- Nickname :: ‘Clean-up crews’
- They are small organelles filled with enzymes, which digest, or break down, lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell.
- They also remove the junk out of the cell.
6. Vacuoles
- Store materials such as water, salts, proteins, and carbohydrates.
- Help the cell in a process of homeostasis [[maintain of a controlled internal environment]]
7. Mitochondria and Chloroplasts
- Both, mitochondria and chloroplasts, are enclosed by two membranes – an outer membrane and an inner membrane. Also they contain their own DNA.
- Mitochondria
· Nickname :: ‘The Power House’
· Mitochondria are organelles that convert the chemical energy stored in food into compounds that are more convenient for the cell to use.
· They come from the cytoplasm of the ovum, or egg cell.
- Chloroplasts
· Chloroplasts are organelles that capture the energy from sunlight and convert it into chemical energy in a process called photosynthesis.
· Contain the green pigment of chlorophyll
· Present mostly in plant cells.
8. Cytoskeleton
- Nickname :: ‘Framework/Skeleton’
- The cytoskeleton is a network of protein filaments that helps the cell to maintain its shape. It also involved in movement.
- Its parts are …
· Microfilaments = threadlike structures made of a protein called actin. They produce tough, flexible framework that supports and helps the cell to move.
· Microtubules = hollow structures made up of proteins known as tubulins. They help the cell to maintain its shape, and also help separate chromosomes.
ð They form spindle fibers, cilia, and flagella -__-++
- Tubulin is also used to form centrioles, which located near the nucleus and help to organize cell division. [[they’re not found in plant cells]]
7-3 Cell Boundaries [[Page.182]]
- All cells are surrounded by a thin, flexible barrier known as the cell membrane.
- Many cells also produce a strong supporting layer around the membrane known as a cell wall.
- The cell membrane regulates what enters and leaves the cell and also provides protection and support.
- The composition of nearly all cell membranes is a double-layered sheet called a lipid bilayer.
· It contains proteins and carbohydrates.
ð Proteins form channels and pumps that help to move material across the cell membrane
ð Carbohydrates allow individual cells to identify one another
PIX OF CELL MEMBRANE
= ok .. don’t mind those confusing-additional parts again -__- =
- Cell walls lie outside the cell membrane.
- The main function of the cell wall is to provide support and protection for the cell.
- Plants cell walls are composed mostly of cellulose.
- One of the most important functions of the cell membrane is to regulate the movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side.
- The cytoplasm of a cell contains a solution of many different substances in water.
· The concentration of a solution is the mass of the solute in a given volume of solution, or mass/volume.
- The particles [[in the cell]] move from an area where they are more concentrated to an area where they are less concentrates in the process of diffusion.
- When the concentration of the solute is the same throughout a system, the system has reached equilibrium.
- Because diffusion depends upon random particle movements, substances diffuse across membrane without requiring the cell to use energy.
- Even when equilibrium is reached, particles of a solution will continue to move across the membrane in both directions.
- Most biological membranes are selectively permeable, meaning that some substances can pass across them and others cannot.
- Water passes quite easily across most membranes, even though many solute molecules cannot. An important process known as osmosis is the result.
- Osmosis is the diffusion of water through a selectively permeable membrane.
- Water can across the membrane in both directions, as a result, there is a net movement of water from the area of high concentration to the area of low concentration [[look at the pix in da book aow la karn if don’t get it]]
- Water will tend to move across the membrane until equilibrium is reached.
· When this happens, the two solutions will be isotonic, which means ‘same strength’
· The more concentrated solution was hypertonic, which means ‘above strength’. The less concentrated solution was hypotonic, or ‘below strength’
- Osmosis exerts a pressure known as osmotic pressure on the hypertonic side of a selectively permeable membrane.
· Osmotic pressure can cause the volume of a cell to increase and becomes swollen. But a cell will burst if only it is in contact with fresh water, which is not very often [[in organism, a cell is in contact with blood not fresh water but in plant, cell wall help protecting it from bursting]]
- Cell membranes have protein channels that make it easy for certain molecules to cross the membrane.
· This cell membrane protein is said to be facilitate, or help, the diffusion of glucose across the membrane.
· The process is called facilitated diffusion.
· But therefore, a new movement of molecules across a cell membrane will occur only if there is a higher concentration of the particular molecules on one side than on the other side. This movement doesn’t require energy.
- Cell sometimes must move materials in the opposite direction – against a concentration difference. This is accomplished by a process known as active transport. It requires energy.
· The active transport of small molecules or ions is generally carried out by transport proteins or pumps that are found in the membrane itself.
ð A considerable portion of the energy used by cells in their daily activities is devoted to providing the energy to keep this form of active transport working.
· Larger molecules can be actively transported by process known as endocytosis and exocytosis.
ð Endocytosis = the process of taking material into the cell by means of infoldings, or pockets, of the cell membrane. The pocket that results breaks loose from the outer portion of the cell membrane and forms a vacuole within the cytoplasm. Two examples of endocytosis are …
~ Phagocytosis ~ extensions of cytoplasm surround a particle and package it within a food vacuole. Then cell then engulfs it.
~ Pinocytosis ~ tiny pockets form along the cell membrane, fill with liquid that the cell take from surrounding environment, and pinch off to form the vacuoles within the cell.
ð Exocytosis = the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.
- Don’t ask me whether I understand da last part [[endocytosis & exocytosis thingy]] .. cause da answer is ‘No. I don’t’ TT^TT
7-4 The Diversity of Cellular Life [[Page.190]]
- A single-celled organism is also called unicellular organism.
· Unicellular organisms grow, respond to the environment, transform energy, and reproduce.
- Organisms that are made up of many cells are called multicellular.
· Cell throughout an organism can develop in different ways to perform different tasks. This process is called cell specialization.
ð Ex. In animals, red blood cells are specialized to transport oxygen. Cell specialized to produce proteins are found in the pancreas.
ð Another ex. for animal cells is human ability to move which is the result of specialized structure of muscle cells.
ð Ex. In plants, ‘guard cells’ regulate the change of gases through tiny opening on the leaves.
- The levels of organization in a multicellular organism are individual cells, tissues, organs, and organ system.
1. Individual cells
2. Tissues = a group of similar cells that perform a particular function.
ð Most animals have four types of tissue :: muscle, epithelial, nervous, and connective tissue.
3. Organs = many groups of tissues that work together.
Ex. there are nerve tissues, connective tissues, and muscle tissues within a muscle.
4. Organ system = a group of organs that work together to perform a specific function.
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