Topic 2 - Cells as the Basis of Life Flashcards
What is cell theory?
Cell theory describes that:
All living organisms are composed of one or more cells.
Cells are the basic structural and functional units of life.
All cells arise from pre-existing cells.
Cells require and use energy.
Cells contain genetic information which is hereditary (passed down to subsequent generation).
What are the characteristics of living things?
They:
- are complex with an organised structure
- take in energy from surroundings and use it to perform living functions
- have an internal composition that is chemically different from the external environment
- respond to stimuli
- reproduce themselves
- grow and develop
The cell is the smallest unit that fits all of these criteria (viruses do not count as they do not reproduce themselves or grow).
How is the cell membrane composed?
The cell membrane is composed of a phospholipid bilayer (hydrophilic head and hydrophobic tail) with protein molecules embedded throughout. It is approximately 8 nanometers thick.
What are the functions of the cell membrane?
- separates the intracellular environment from the extracellular environment, ensuring that they remain chemically different (concentration of subunits, pH and the presence of ions).
- regulates the passage of substances in and out of the cell.
- enable cells to recognise one another and certain ligands, as the polysaccharides attached to the proteins act as receptors
- enable the attachment of the cytoskeleton
How is the cell membrane described by the fluid mosaic model?
The cell membrane is a fluid mosaic model composed of a phospholipid bilayer with protein molecules embedded in and through the layer at various points. The fluid is representative of the constantly moving phospholipids, whilst the mosaic describes the proteins embedded in the membrane.
What are the characteristics of prokaryotic cells?
- generally smaller than eukaryotes
- can be as small as one micrometer
- relatively unspecialised
- cell is contained within a plasma membrane
- plasma membrane is usually surrounded by a cell wall
- cell wall often have short pili projecting from them, and sometimes larger flagella
- no membrane-bound organelles
- ribosomes are present
- do not have a nucleus, as DNA exists within the cytoplasm as a single, circular chromosome (and occasionally in rings called plasmids)
- all single-celled
Are bacteria prokaryotic or eukaryotic?
Prokaryotic.
What are the characteristics of eukaryotic cells?
- more organised and specialised internally
- larger than prokaryotes
- size generally ranges between 10-100 micrometers
- contain membrane bound organelles
- each organelle has a specific task within the cell
- contains a nucleus that stores the cell DNA
- have a cell membrane
- some also have a cell wall
What are the common types of eukaryotes?
Protists, plants, animals and fungi.
How is the nucleus structured?
The nucleus contains two membrane layers called the nuclear envelope. Within this nuclear envelope are many small holes lined with proteins called nuclear pores, allowing movement in and out of the nucleus.
What is the function of the nucleus?
The nucleus stores the cell DNA, containing the hereditary information and instructions for functionality.
What is chromatin and how does it it effect DNA?
A protein called chromatin is associated with nuclear DNA. During replication, chromatin condenses the long strands of DNA into the shorter X-shaped chromosomes.
What is the location and function of the nucleolus?
The nucleolus is located within the nucleus, and the is site for ribosome production.
How is the chloroplast structured?
Chloroplast contain two outer membranes, with a system of membranous flattened sacs called thylakoids inside. These thylakoids are stacked to form grana (singular - granum). The fluid surrounding the grana is called stroma.
What is the function of the chloroplast?
The thylakoid membranes contain chlorophyll, the pigment required for photosynthesis. Thus, it is the site for photosynthesis.
What are chloroplasts derived from?
Derived from a family of closely related plant organelles called plastids.
How is the mitochondria structured?
The mitochondria contains two membranes, an outer and an inner which are highly folded into cristae. They also contain their own circular DNA, which resembles prokaryotic DNA.
What is the function of mitochondria?
The mitochondria is involved in cellular respiration (use of oxygen and glucose to release energy and store it in Adenosine Triphosphate - ATP). Therefore, cells that require lots of energy contain lots of mitochondria.
What are mitochondria derived from?
Evidence suggests that mitochondria were once bacteria that were incorporated into cells, hence the DNA that resembles prokaryotic DNA.
Which organelles are present in which type of cells?
Nucleus - plant, animal and fungi
Nucleolus - plant, animal and fungi
Chloroplast - plant
Mitochondria - plant, animal and fungi
Vesicles - plant, animal and fungi
Vacuoles - plant, animal and fungi
Lysosome - animal
Rough Endoplasmic Reticulum - plant, animal and fungi
Smooth Endoplasmic Reticulum - plant, animal and fungi
Golgi Body - plant, animal and fungi
Ribosomes - plant, animal and fungi
Cytoskeleton - plant, animal and fungi
How are vacuoles structured?
Vacuoles are fluid filled space bound by a membrane. They are part of the endomembrane system.
What is the function of vacuoles in plant cells?
Vacuoles store organic compounds such as proteins and sugars that are stockpiled in storage cells (cells ready for germination). They can also be the main storage for inorganic molecules such as ions. Plants cells may also use vacuoles as storage for metabolic wastes that would endanger the cell if they remained in the cytoplasm. Vacuoles have a major involvement in growth as water is absorbed, elongating the vacuole which allows the cell to become larger.
What is the function of vacuoles (vesicles) in animal cells?
Non-plant cells contain more, smaller vacuoles called vesicles. There are two types: food vacuoles (lysosomes) and contractile vacuoles. Lysosomes contain enzymes that digest macromolecules when a cell engulfs a particle (phagocytosis). Contractile vacuoles pump excess water out of the cell.
What is the function of vacuoles in fungi?
Some fungi cells have large vacuoles, with a similar function to those in plant cells. These vacuoles act as storage sites but can also contain enzymes that break down compounds.
How is the endoplasmic reticulum structured?
The endoplasmic reticulum is a system of membranes (endomembrane system) that extends through the cytoplasm. It is a series of “passages” that are important for the transportation of materials around the cell. If ribosomes are attached, it is the rough endoplasmic reticulum. If ribosomes are not attached, it is the smooth endoplasmic reticulum.
What is the function of the rough endoplasmic reticulum?
The rough endoplasmic reticulum is the site for protein and membrane synthesis.
What is the function of the smooth endoplasmic reticulum?
The smooth endoplasmic reticulum is involved in the synthesis of lipids and the detoxification of drugs, poisons and alcohol.
How is the Golgi apparatus structured?
The Golgi apparatus is composed of flattened sacs and layered membranes.
What is the function of the Golgi apparatus?
The Golgi apparatus is involved in the packaging and secretion of proteins and carbohydrates. Cells that are specifically involved are secretion contain more Golgi bodies. Vesicles containing carbohydrates bud off from the Golgi body and move to the cell membrane where they fuse and release their contents outside the cell - exocytosis.
How is the cytoskeleton structured?
The cytoskeleton is a network of fibres throughout the cytoplasm. It is composed of three main filaments: microtubules, intermediate filaments, and microfilaments.
What is the function of the cytoskeleton?
The cytoskeleton:
- gives cells their shape
- is involved in cell movement
- holds organelles in place
- strengthens the cell
- acts like a cellular skeleton (but can be dismantled and reassembled in a new location)
- enables cells to hold specialized shapes or surfaces, mainly to increase surface area
How are microtubules structured and what is their specific function?
Microtubules are the thickest filament of the cytoskeleton. They are straight hollow rods that elongate by adding Tubulin molecules to its ends. It can be disassembled to be built elsewhere in the cell. They act as tracks that organelles equipped with motor molecules can move along. Microtubules are involved in the separation of chromosomes during mitosis and also compose the centrioles.
How are intermediate filaments structured and what is their specific function?
Intermediate filaments are the intermediate size of cytoskeleton filament. They are a diverse class of cytoskeleton elements, constructed from different subunits of the Keratin protein family. They are a more permanent fixture, that reinforce the shape and fixture of the organelles. They are also specialized for bearing tension.
How are microfilaments structured and what is their specific function?
Microfilaments are the smallest cytoskeleton filaments. They are solid rods made of the globular protein Actin. They are involved in intracellular movement, and also act as support in eukaryotes.
How are ribosomes structured?
Ribosomes are composed of a large and small subunit that together “read” mRNA.
What is the function of ribosomes?
Ribosomes are the site where cells assemble proteins. They do so from two different locations: free (floating around the cytoplasm) and bound (attached to the endoplasmic reticulum). Cells with a high rate of protein synthesis contain more ribosomes.
How do the proteins produced by ribosomes differ in response to the ribosome location?
Ribosomes are either free (floating around the cytoplasm) or bound (attached to the endoplasmic reticulum). Most proteins produced by free ribosomes function within the cytoplasm. Bound ribosomes produce proteins that are generally destined for inclusion into the membrane or packaging into organelles such as lysosomes.
How is energy defined?
Energy is defined as the capacity to do work.
Why do cells require energy?
Cellular processes such as movement, active transport, exocytosis, endocytosis, phagocytosis, and the synthesis of macromolecules all require energy. This enables the cell to grow, repair, reproduce and function normally.
How is energy obtained from the environment?
Energy must either be obtained in a physical or chemical form. Some cells can use sunlight as a physical form of energy, whilst others take in energy-rich compounds in the form of chemical energy. In both cases, energy is transformed so that is it useful. For example, plant cells have chloroplasts that transform light energy into chemical energy. Whereas, animals have muscles that convert chemical chemical energy into movement.
What is the difference between autotrophs and heterotrophs?
Autotrophs are self feeding. Most of them use sunlight as a physical energy source to store chemical energy (e.g. photosynthesis).
Heterotrophs gain their chemical energy from another source (e.g. eating to create physical energy).
What is photosynthesis (using an equation) and where does it occur?
Photosynthesis is the conversion of light energy to chemical energy.
6CO2 (g) + 6H20 (l) –light/chlorophyll–> C6H12O6 (aq) + 6O2 (g)
carbon dioxide + water –> glucose + oxygen
It occurs in the chloroplasts of plant cells, as chlorophyll absorbs light in the granum. Enzymes that catalyse the reaction are found in the granum and stroma.
How is energy transformed during respiration?
The breakdown of glucose, in the presence of oxygen, releases energy. This is because the amount of energy required to break the chemical bonds in the reactants (glucose and oxygen) is less than the energy released when the bonds in the products (carbon dioxide and water) are formed. Some of this energy is used by the cell to do work, whilst the rest is lost as heat.
What is ATP?
Adenosine Triphosphate (ATP) is one of the most important energy storage compounds in the cell. ATP (like RNA) has the nitrogen base Adenine bonded with a ribose sugar. This is bonded to three phosphate groups. The third bond is unstable and can be hydrolysed (broken down with water) to form Adenosine Diphosphate + Pi and energy.
What is the ATP cycle?
ATP can be converted to ADP + Pi through hydrolysis, and this process releases energy. ADP + Pi can be converted back to ATP, however, this process requires energy.
How is ATP used and how is it acquired?
Cells use ATP continuously for cellular processes, but they also produce it continuously. The energy required to refuel ATP from ADP + Pi comes from cellular respiration.
What is aerobic respiration (using an equation) and where does it occur?
Most autotrophs and heterotrophs transform stored chemical energy into a form they can use through aerobic respiration. Aerobic respiration uses oxygen to break down glucose into carbon dioxide and water:
C6H12O6 (aq) + 6O2 (g) –> 6CO2 (g) + 6H2O (l)
glucose + oxygen –> carbon dioxide + water
Aerobic respiration occurs in the mitochondria.
How many ATP molecules are produced in aerobic respiration?
One molecules of glucose produces 36 ATP molecules when oxygen is used.
What is anaerobic respiration (using an equation) and where does it occur?
Anaerobic respiration, also known as fermentation, is an alternate pathway to aerobic respiration. This process happens in the cytoplasm of cells. In plants and yeasts, ethanol and carbon dioxide are produced (ethanol fermentation):
C6H12O6 (aq) –> 2C2H5OH (aq) + 2CO2 (g)
glucose –> ethanol + carbon dioxide
In animals, anaerobic respiration produces lactic acid (lactic acid fermentation):
C6H12O6 (aq) –> 2C3H6O3 (aq)
glucose –> lactic acid
How many ATPs do anaerobic pathways produce?
Both anaerobic pathways, ethanol fermentation and lactic acid fermentation, produce 2 ATP molecules per glucose.
What are the properties of ATP that make it ideal as the energy-carrying molecule in cells.
- small and water soluble (it is easily transported around the cell)
- renewable (ATP can be easily regenerated from ADP, Pi and the energy released from aerobic respiration)
- weak bond between the last phosphate (easily broken to release energy)
What are limiting factors?
A factor which limits the amount of product formed and, therefore, the rate of reaction.
What are the limiting factors of photosynthesis?
Limiting factors of photosynthesis include temperature, water availability, light intensity, and carbon dioxide concentration.
Why does aerobic and anaerobic respiration produce a different number of ATP molecules?
Harvesting energy occurs in a series of steps. Both processes begin with glycolysis, however, anaerobic respiration does not continue through the Krebs cycle. This means that the yield of energy (ATP) is lower for anaerobic respiration, as the glycolysis process only uses 2 ATPs and produces 4 - net release of 2 ATPs.
What are the effects of releasing energy in steps (metabolic pathway)?
- intermediate compounds can be used for other processes
- the reaction does not occur too quickly and burn up the cell
- the amount of energy stored in ATP molecules is maximised
- however, some energy is lost as heat (but it is the least possible that is lost)
- maintains optimum temperatures for cellular processes
What are cellular inputs and outputs?
In order to survive, cells require an input of matter (including gases, simple nutrients, and ions) and the removal of wastes.
What are the differences in inputs and outputs of autotrophs and heterotrophs?
Autotrophs make large, energy-rich organic compounds from small inorganic compounds. Heterotrophs need lots of inorganic compounds as well as the larger organic compounds that they cannot make. The products of metabolic pathways also differ depending on the type of respiration being undertaken.
Example of autotrophs forming organic compounds from inorganic compounds.
Inorganic compounds taken in by autotrophs include water and carbon dioxide, which are used to make glucose in photosynthesis. Nitrate/nitrite ions, phosphate ions and sulfate ions are absorbed by plants from the soil. These combine with the glucose to make lipids, amino acids, bases and nucleotides.
Why is the cell membrane important in terms of intracellular VS extracellular environment?
The cell membrane is important to ensure that the intracellular environment remains chemically different to the extracellular environment. Many subunits are present within the cell at high concentrations but not external to the cell. Acidity must also be kept within a narrow range. The presence of ions may also differ.
What is diffusion?
Diffusion is the movement of one substance from an area of high concentration to an area of lower concentration. The movement of substances flows with the concentration gradient.
How does equilibrium impact diffusion?
Diffusion will continue until equilibrium is reached. This does not mean the movement of particles stops, rather the movement of particles in one direction will balance the movement of particles in the opposite direction. Under these conditions, the next movement is zero and there is no concentration gradient.
Is diffusion a passive or an active process? Why?
Diffusion is a passive process because it does not require energy. Diffusion of a molecule is unaffected by concentration gradients of other molecules.
What is osmosis?
Osmosis is the diffusion of water from an area of low solute concentration to an area of higher solute concentration.
Is osmosis a passive or an active process? How does it impact a cell?
Osmosis is a passive process as it does not require energy, due to the flow being with the concentration gradient. Osmotic pressure is what helps maintain the shape of animal cells and provides support in plant cells.
