Basic Components of Living Systems Flashcards
Specification reference: 2.1.1
What is a microscope?
Instrument that enables you to magnify and object many times
Cell theory
- Plant and animal tissue is composed of cells
- Cells are the basic unit of all life
- Cells only develop from existing cells
Positives of light microscopes
- Easily available
- Cheap
- Portable
- Can be used to observe dead and living organisms
How many lenses do compound light microscopes have?
- Objective lens: Placed near the specimen
2. Eyepiece lens: Where the specimen is viewed
Objective Lens
Produces a magnified image which is magnified by the eyepiece lens. Configuration allow more magnification and less chromatic abberation
Magnification
How many times larger the image is than the actual size of the object being viewed.
Resolution
Ability to see individual objects as separate entities. Which then produces a detailed image.
Diffraction
Tendency for light waves to spread as they pass through samples.
How can resolution be increased?
By using beams of electrons which have a wavelength a thousand times shorter than light.
Magnification Equation
size of image / actual size of the image
Electron microscopy
- A beam of electrons with a wavelength of less than 1 nm is used to illuminate species.
- More detail of the ultra structure can be seen as electrons have smaller wavelength than light waves
- Magnification of x 500000 and will still have a clear resolution
What are the two types of electron microscopes?
Transmission electron microscopes
Scanning electron microscopes
Transmission Electron Microscope (TEM)
A beam of electrons is transmitted through a specimen and focused to produce an image. This has the best resolution with resolving power of 0.5 nm.
Scanning Electron Microscope (SEM)
A beam of electrons sent across the surface of the specimen and the reflected electrons are collected. The resolving power is from 3-10nm (not as good as TEM). Produces a 3D image.
Ultrastructure
Features that can be seen with an electron
Artifacts
Visible structure structural detail caused by processing the specimen and not a feature of a specimen
Laser scanning confocal
Moves a single spot of focused light across the specimen (point illumination). This causes fluorescence from the components labeled with a ‘dye’.
Conventional optical microscopes
Use visible light to illuminate specimens and a lens to produce a magnified image.
Fluorescent microscopes
Have a higher light intensity is used to illuminate a specimen that has been treated with a fluorescent dye.
Fluorescence
The absorption and re-radiation of light. Light of a longer wavelength and lower energy is emitted and used to produce a magnified image.
Cells
The basic unit of all living things
What are the two types of cell?
Prokaryotic and Eukaryotic
Prokaryotes
Are single-celled organisms with a simple structure of just a single undivided internal area called the cytoplasm (composed of cytosol which is made of water and organic molecules)
Eukaryotes
Made up of multicellular organisms (animals, plants, fungi). They have a more complicated structure containing a membrane-bound nucleus and cytoplasm which contains many membrane-bound cellular components.
Metabolism
Involves synthesis (building up) and the breaking down of molecules.
Cytoplasm
Reactions take place in the cytoplasm. The cytoplasm separates the cell from its external environment by a cell-surface membrane. Cytoplasm provides distinct environments and conditions for different cellular reactions.
Organelles
Membrane-bound components
Membranes
Selectively permeable and control the movement of substances in and out of the cell and organelles. Membranes are fragile.
Nucleus
Contains coded genetic material in the form of DNA molecules
DNA
Directs the synthesis of all proteins required by the cell. DNA controls the metabolic activities
Nuclear envelope
DNA contained in a double membrane to protect it from damage in the cytoplasm. It contains Nuclear pores which allow molecules to move in and out of the nucleus.
Nucleolus
An area within the nucleus responsible for producing ribosomes. It is composed of protein and RNA. It is used to produce rRNA which is combined with proteins for photosynthesis
Mitochondria
A site for the final stages of cellular respiration, where energy stored in the bonds of a complex organic molecule made available for the cell to use by the production of ATP,
How many membranes do Mitochondria have
2.
The inner membrane of the mitochondria
Folded to form structures called cristae and the fluid interior is called the matrix. The membrane forming the cristae contains enzymes used in aerobic respiration.
Does Mitochondria have its own DNA?
Yes, it is called the mitochondrial (mt) DNA. Mitochondria can produce their own enzymes and reproduce themselves.
Vesicles
Membrane sacs that have storage and transport roles. They consist simply of a single membrane with fluid inside. Vesicles are used to transport materials into the cell.
Lysosomes
Are specialized forms of vesicles that contain hydrolytic enzymes. They are responsible for breaking down waste material in cells (including old organelles)
Role of lysosomes
They have a role in the immune system as they are responsible for breaking down pathogens ingested by phagocytic cells. They play a role in apoptosis (cell death)
Cytoskeleton
Present throughout the cytoplasm of all eukaryotic cells. It is a network of fibers necessary for the shape and stability of a cell. It controls cell movement + movement of organelles within cells.
What are the three components of the cytoskeleton
- Microfilaments
- Microtubles
- Intermediate fibres
Microfilaments
Contactile fibre formed from the protein actin. These are responsible for cell movement and cell contarction during cytokinesis
Microtubules
Globular tubulin proteins polymerize to form tubes that are used to form scaffold-like structures that determine the shape of the cell. They act as tracks for movement of organelles including vesicles around the cell. Spindle fibers which have a role in the physical segregation of chromosomes in the cell division are composed of microtubules.
Intermediate fibers
Provide mechanical strength to cells and make them maintain their integrity
Centrioles
A component of the cytoskeleton present in most of the eukaryotic cells (exception of fungi and flowering plants). Composed of microtubules. Two associated centrioles form the centrosome, which is involved in the assembly and organization of the spindle fibers during cell division.
Flagella
Are extentions that protrude from some cell types. Enable cells to have motility - in some cells.
In some cells they are used as a sensory organelle detcting chemical changes in the cell’s environment
Cillia
- Cillia can be mobile or stationary.
- Each cilium contains two central microtubles (black circles) surrounding by the 9 pairs of microtubles arranged by a wheel (9+2 arrangement)
- Pairs of the parallel microtubles slide over each other causing cilia to move in beating motion
Stationary Cillia
- Stationary cilia are present on the surface of many cells and have important functions in sensory organs
Mobile Cilia
- Mobile cilia beat in a rhythmic manner creating a current and cause fluids or objects adjacent to the cell to the move (trachea and fallopian tubes)
What does DNA associate with…
Histones to form a complex called chromatin. Chromatin coils and condenses to form structures known as chromosomes (only visible when cells are being prepared to divide)
Endoplasmic Reticulm
Network of membranes enclosed in flattened sacs called cisternae
RER
Has ribosomes bound to the surface and is responsible for the synthesis and transport of proteins
SER
Responsible for storage and lipid and carbohydrate production
Golgi Apparatus
Compact structure formed of cisternae which doesn’t contain ribosomes.
Role of the Golgi Apparatus
Modifies proteins and packages them into vesicles.
Steps of protein synthesis: Step 1
Proteins are synthesised on the ribosomes bound to the endoplasmic reticulum
Steps of protein synthesis: Step 2
They pass into the cisternae (ER) and are packaged as transport vesicles
Steps of protein synthesis: Step 3
Vesicles containing newly synthesised proteins move towards the Golgi apparatus via the transport function of the cytoskeleton
Steps of protein synthesis: Step 4
Vesicles fuse with the cis face of the Golgi apparatus and proteins enter. The proteins are structurally modifies before leaving the Golgi apparatus in vesicles from its trans face
Steps of protein synthesis: Step 5
Secretory vesicles carry proteins that are released from the cell. Vesicles move towards + fuse with the cell-surface membrane releasing its contents via exocytosis. Some vesicles form lysosomes (which contain hydrolytic enzymes)
