Biology Unit 1 Cells, exchange and transport
Covering the learning objectives in Biology AS OCR book unit 1
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- Created by: Agustin Quesada
- Created on: 16-04-11 02:42
Cells- Structure and function
Nucleus
- Largest organelle
- Surrounded by nuclear envelope with nuclear pores
- Dense spherical structure
- Has a nucleolus inside
- House nearly all the cell's genetic material
- Cromatic consists of DNA and proteins
- The nucleolus makes RNA and ribosomes
Golgi apparatus
- A stack of membrane-bound, flattened sacs
- Receives proteins from the ER and modifies them
- Packages the modified proteins into vesibles that can be transported
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Cells- Structure and function
Endoplasmic reticulum (ER)
- Series of flattened, membrane-bound sacs called cisternae
- The rough endoplasmic reticulum (RER) is studded with ribosomes
- RER transports proteins that were made on the attached ribosomes
- SER is involved in making the lipids needed by cells
Mitochondria
- Two membranes separated by a fluid-filled space
- Ineer membrane is highly folded to form cristae
- The central part is called matrix
- Site where ATM is produced during respiration
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Cells- Structure and function (2)
Cloroplasts
- Only found in plant cells and some protoctists
- Two membranes separated by a fluid-filled space
- Have an elaborate network of flattened membrane sacs called thylakoids
- A stack of thylakoids is called a granum
- Clorophyl molecules are present on the thylakoids
- Site of photosynthesis in plant cells
Lysosomes
- Spherical sacs surrounded by a single membrane
- Contain powerful digestive enzymes to break down materials
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Cells- Structure and function (2)
Ribosomes
- Tiny organelles
- Some in the cytoplasm and some bound to the RER
- They consist of two subunits
- Site of protein synthesis
- Acts as an assembly line where mRNA is used to assemble proteins
Centrioles
- They are microtubules (small tubes of protein fibres
- They form the spindle fibres which move chromosomes during nuclear division
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Cells- Microscopes
Light microscope
- Maximum magnification of x1500
- low resolution (200nm)
Transmission electron microscope (TEM)
- Final image is two dimensional
- Maximum magnification of x500 000
- Electrons pass through the sample and show contrast in different tissues
- Resolution of 0.1 nm
Scanning electron microscope (SEM)
- Final image is a three dimensional image of the surface
- Maximum magnification is x100 000
- Electrons are bounced off the surface
- Resolution of 0.1 nm
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Cells- Microscopes
- A microscopic ruler (stage micrometer) can be placed on the microscope
- The eye piece can be fitted with a graticule
- The graticule and stage micrometer can be used to measure samples
- Actual size = image size/ magnification (I AM triangle)
- Magnification- the number of times greater an image is than the object
- Resolution- the ability to distinguish that two points are separated
- Staining and sectioning are used to prepare samples
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Crossing membranes
- Roles of membranes:
-
- separate cell contents from the outside environment
- separate cell contents from the cytoplasm
- cell recognition and signalling (with complementary receptors)
- holding the components of some metabolic pathways in place
- regulating the transport of materials in and out of cells
- Membranes are about 7-10 nm thick
- The phospholipid bilayer is the basic structural component of plasma membranes consist of two layers of phospholipid molecules
- A pospholipid molecule is formed of a hydrophilic phosphate head and two hydrophobic fatty acid tails, forming the fluid mosaic model
- Increasing the temperature of membranes makes the molecules have more kinetic energy and makes the membrane more fluid and leaky
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Crossing membranes- transport
- They are partially permeable
- Involved in cell signalling:
- Glycolipid- a lipid with a carbohydrate molecules attached
- Glycoprotein- a protein with carbohydrate molecules attached
- Cholesterol gives the membranes stability and makes the membrane impermeable to water molecules and ions
- Passive processes (no ATP used)
- Diffusion- down a concentration gradient, for lipid soluble or very small molecules, through the lipid bilayer
- Facilitated diffusion- down a concentration gradient, charged or hydrophilic molecules or ions, via carrier or channel proteins
- Osmosis- down a water potential gradient, through bilayer or protein pores
- Active processes (using ATP)
- Active transport- against a concentration gradient, via carrier proteins which change shape using ATP
- Endocytosis and exocytosis- bulk transport of materials via vesicles that fuse with or break from the cell surface membrane
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Crossing membranes- osmosis
- There is a net movement from the region with a higher water potential to a region with lower water potential
- If the water potential is the same there will be movement across, just no net movement
- The more solutes in a solution, the lower the water potential is
- Water moves in the cell
- Animal cell- the cell will swell and eventually burst open (haemolysed)
- Plant cell- the cell will swell and eventually be turgid (due to support of the cell wall)
- Water moves out of the cell
- Animal cell- the cell will shrink and eventually be crenated
- Plant cell- cell membrane pulls away from the cell wall (it is plasmolysed)
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Cells- Mitosis
- Mitosis is the process of nuclear division where two genetically identical nuclei are formed from one parent cell nucleus
- The daughter cells are genetically identical both to each other and to the parent cell
- Chromatin- DNA wrapped around proteins called histones, they remain together at a point called centromere
- A pair of two replica DNA strands is called a pair of sister chromatids
- In plant cells only meristem cell can divide this way
- In plant cells there are no centrioles, tubulin protein threads are used
- In animal cells cytokinesis starts from the outside (nipping in) but in plant cells cytokinesis starts with the formation of a cell plate where the spindle equator was (outwards)
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Cells- Mitosis
- Stages:
-
- Interphase- It has two growth stages (G1 and G2) and stage S which is DNA synthesis (replication of DNA)
-
- Mitosis
- Prohase- chromosomes shorten and thicken and are now visible, nuclear envelope breaks down, centriole divides into two and each moves to opposite poles
- Metaphase- chromosomes attach to a spindle by their centromere
- Anaphase- spindle fibres shorten pulling the sister chromatids towards the poles
- Telophase- spindle breaks down and disappears, chromosomes uncoil and are no longer visible, nuclear envelope reforms
- Mitosis
-
- Cytokinesis- the cytoplasm divides or cleaves
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Cells- specialisation
- Differentiation- the changes occurring in cells of a multicellular organism so that each different type of cell becomes specialised to perform a specific function (e.g. erythrocytes, lysosomes)
- Tissues- a collection of cells that are similar to each other and perform a common function (e.g. xylem, phloem, epithelial, nervous)
- Organs- a collection of tissues working together to perform a particular function (e.g. leaves, liver)
- Organ systems- made up a number of organs working together to perform an overall life function (e.g. excretory system, reproductive system)
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