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Cells

91156Demonstrate understanding of life processes at the cellular level

Full Topic Posters

These have been made by Benjamin Himme from https://www.pathwayz.org/ (Another great learning site)

Introduction to the topic


Some excellent started interactive animations on cells!

Life is both wonderful and majestic. Yet for all of its majesty, all organisms are composed of the fundamental unit of life, the cell. The cell is the simplest unit of matter that is alive. 
This standard is looking at the processes that happen at the cellular level and how factors such as availability of resources and the activity of enzymes can affect the cell. For this topic you do need to understand DNA and protein synthesis and the process of DNA replication so I recommend looking at Gene expression as well (to the left).


The basics..

Living organisms are composed of one or more cells
Cells are the smallest unit of life
All cells come from pre-existing cells

The cell theory has amassed tremendous credibility through the use of the microscope in the following:
Robert Hooke- studied cork and found little tiny compartments that he called cells
Antonie van Leeuwenhoek- observed the first living cells, called them 'animalcules' meaning little animals. I'm a little bit disappointing that this name didn't stick.
Schleiden- stated that plants are made of 'independent, separate beings' called cells
Schwann- made a similar statement to Schleiden about animals

A great intro video to the topic

And Mr Khan also explains the parts very well (:

A good diagram showing the differentiation of cells in the human body (Click on it to make it bigger).

http://lgfl.skoool.co.uk/content/keystage3/biology/pc/learningsteps/SPALC/launch.html

General introduction links

A general Cells link

Cell size and scale as compared to a rice grain. Quick flash animation.
Compare sizes of cells - different types of cells are different sizes. Watch the animation.

Click on the following animal cell to see more detail.


Animal vs. Plant cells

There are many similarities and differences between animal and plant cells.  
Make sure you know these.

SimilaritiesDifferences
1. Have a nucleus1.  Plant cells have a cellulose cell wall
2. Have a cytoplasm2.  Plant cells have a vacuole containing cell sap
3. Have a cell membrane3.  Plant cells have chloroplast
4. Contain mitochondria4.  Many plant cells have a box-like shape whilst animal cell shape varies
5. Contain ribosomes5.  Plant cells have the nucleus to the side of the cell, animal cells have a nucleus in the middle



Life processes at the cellular level


Metabolism chemical reactions inside the cell, including cell respiration to release energy.
In cells this reaction can be aerobic (involve oxygen) or anaerobic (involve no oxygen).

Response perceiving and responding to changes in the environment. It is important for a cell to be able to respond to unfavorable conditions and either move to better or change the conditions using active or passive transport.

Homeostasis keeping conditions inside the organism within tolerable limits. 

Growth an irreversible increase in size. The majority of somatic (body) cells in ideal conditions will reach a size and divide asexually in the process of binary fission. 

Reproduction producing offspring either sexually or asexually
Nutrition obtaining food, to provide energy and the materials needed for growth
Defense protection against enemies

LearnCOACH video


Photosynthesis

(2014) Photosynthesis occurs in plants / chloroplasts, and is a chemical reaction that splits water molecules into hydrogen and oxygen. Carbon dioxide is joined to the hydrogen to form glucose. The excess oxygen is released as by-product.
6 CO2 + 6 H2O → 6(CH2O) + 6 O2
sugar

An excellent starter animation can be found here
Another great interactive learning module here
Some L2 Biology notes here


Structure of leaves and photosynthesis

Leaves are flat and thin.

The epidermis is usually transparent (epidermal cells lack chloroplasts) and coated on the outer side with a waxy cuticle that prevents water loss which would decrease the rate of photosynthesis.

The location of cells containing most chloroplasts are found near the top of the leaf in (palisade) long cylindrical cells, with the chloroplasts close to the walls of the cell. These factors combine and lead to more light being received where it can be used to maximize the rate of photosynthesis.

The slight separation of the cells provides maximum absorption of carbon dioxide.

Beneath the palisade layer is the spongy mesophyll. The cells of the spongy layer are more rounded and not so tightly packed. There are large intercellular air spaces. This maximizes the rate of diffusion of the gases during photosynthesis. (CO2 entering the leaf and O2 leaving it.)

Specialised guard cells mainly on the lower leaf epidermis function to control the movement of gases and water loss.

Chloroplast as the organelle associated with photosynthesis and their structure also maximises the rate at which it can occur: flat stacks of thylakoids have an increased surface area for the absorption of light.

Stroma is a clear fluid, which doesn’t block the light.

Chloroplasts have thin membranes / large surface area for absorption of light.

The combination of the cell and organelle structure and location collectively helps to keep photosynthesis at its maximum potential rate.


A great video from LearnCOACH


Limiting factors of Photosynthesis


(2014) The rate of photosynthesis will always correspond to the factor which is in least supply.

Other factors that affect the rate are light intensity / availability / quality, wave length of light, amount of chlorophyll / chloroplast number, temperature, enzyme concentration, nutrients.

Examples, but could discuss other factors:

Generally warmer temperatures are better than cooler temperatures for photosynthesis. This means enzymes can collide more with substrates and more chemical reactions can occur. However, if the temperature increases too much, the enzyme may denature, resulting in the active site changing shape (no longer fitting the substrate), in which case the chemical reactions would stop, and photosynthesis rate decrease / stop.

Different intensities of light provide different amounts of energy / photons.

Different wavelengths / colours of light provide different amounts of energy / photons. Least energy from Green light as it is reflected.

Plant nutrient exposure will affect the production of enzymes. As amino acids are required for enzyme construction / protein synthesis, if essential amino acids are not taken up by the plant, the plant may not be able to construct the enzymes necessary for photosynthesis to occur (thus decreasing the plants rate of photosynthesis). As well as this, the amount of nutrients, such as potassium and nitrates, also affects the rate of photosynthesis. These nutrients could be used by enzymes as co-factors. If the co-factors / nutrients are limited, this would limit chemical reactions and the rate of photosynthesis.

The amount of water or CO2 available to the plant will affect the rate of photosynthesis. If the plant does not have enough water, the plant will be deprived of H or CO2(so will be unable to construct a glucose molecule), and thus lower photosynthesis rate.

Increased amount of CO2 will increase the rate of photosynthesis to a certain limit, after which a further increase in its amount will no longer increase the rate any further. This is when the other factors necessary for photosynthesis, such as light, become “limiting factors”; that is, those other factors also need to increase to bring about a further increase in the rate.

Respiration

Defined as converting biochemical energy from nutrients into useable energy (ATP) and then the release of waste products.

Introduction

Cellular respiration is the process by which the chemical energy of "food" molecules is released and partially captured in the form of ATP. Carbohydrates, fats, and proteins can all be used as fuels in cellular respiration, but glucose is most commonly used as an example to examine the reactions and pathways involved.

A great video from LearnCOACH


Definition may be given as: 

‘To convert biochemical energy from nutrients into useable energy (ATP) and then release waste products.”
A great introduction to Respiration in the video below.




The purpose of aerobic respiration is to release energy from food. It is needed for metabolism, growth, movement etc.

C6H12O6 + 6 O2 6 CO2  + 6 H2O + Energy (ATP). Can also state the reactants and products in words.

(May mention that fats and proteins can also be consumed as reactants.)

Glucose is consumed by animals or made by plants. Glucose molecule is broken down and reacts with oxygen (inhaled) to form ATP / energy. Water and carbon dioxide are by-products of the reaction.

Aerobic respiration takes place in mitochondria.


We can divide cellular respiration into three metabolic processes: glycolysis, the Krebs cycle, and oxidative phosphorylation. Each of these occurs in a specific region of the cell.

1. Glycolysis occurs in the cytosol.

2. The Krebs cycle takes place in the matrix of the mitochondria.

3. Oxidative phosphorylation via the electon transport chain is carried out on the inner mitochondrial membrane.


The Pathways of Respiration

In the absence of oxygen, respiration consists of two metabolic pathways: glycolysis and fermentation. Both of these occur in the cytosol.
In glycolysis, the 6-carbon sugar, glucose, is broken down into two molecules of a 3-carbon molecule called pyruvate. This change is accompanied by a net gain of 2 ATP molecules and 2 NADH molecules.
The Krebs cycle occurs in the mitochondrial matrix and generates a pool of chemical energy (ATP, NADH, and FADH2) from the oxidation of pyruvate, the end product of glycolysis.

Pyruvate is transported into the mitochondria and loses carbon dioxide to form acetyl-CoA, a 2-carbon molecule. When acetyl-CoA is oxidized to carbon dioxide in the Krebs cycle, chemical energy is released and captured in the form of NADH, FADH2, and ATP.
the chemical energy stored in glucose generates far more ATP in aerobic respiration than in respiration without oxygen (glycolysis and fermentation).

Each molecule of glucose can generate 36-38 molecules of ATP in aerobic respiration but only 2 ATP molecules in respiration without oxygen (through glycolysis and fermentation).

Mitochondria have an outer membrane, which regulates the passage of materials in and out of the organelle.

The inner mitochondrial membrane is compartmentalised into numerous cristae, which expands its surface area thereby enhancing its ability to produce ATP. Mitochondria from cells that have a greater demand for ATP, such as muscle cells, contain even more cristae.

The matrix is the fluid-filled space enclosed by the inner membrane, containing many enzymes, which can function on the large surface area created by the cristae. The number of mitochondria in a cell varies widely by organism and tissue type. There are more in animal cells than plant cells. Many cells have only a single mitochondrion, whereas others can contain many more (muscles, glands, etc), even up to several thousand mitochondria (eg, liver cells). Variation in number is related to the energy requirements of the particular cells. The higher the energy demand; the greater the number of mitochondria.

An interesting (unexpected part from the 2014 exam)

Why different numbers of mitochondria are found in different cells

Red blood cells do not contain mitochondria because they have very low (do not require) energy requirements as they only carry out passive processes / transporting O2 / diffusion, OR do not carry out active ones, (such as DNA replication, cell division etc).

(Red blood cells derive energy via glycolysis, which occurs in the cytoplasm.)

Skin cells have a couple of hundred mitochondria because they need to divide often. They are not involved in movement, so do not require large amounts of energy.

Liver cells contain 1000–2000 mitochondria because the liver is the involved in digestion / toxin removal which requires a lot of energy, therefore requires large numbers of mitochondria.

The heart muscle contains 5000+ mitochondria because it is constantly moving / contracting throughout a person’s life. Movement requires lots of energy. The heart muscle pumps blood to every organ around the body, therefore it is very important it never stops.

The number of mitochondria in a cell varies widely by organism and tissue type. Red blood cells do not have mitochondria, whereas muscle cells contain up to several thousand mitochondria. Variation in number is related to the energy requirements of the particular cells.

Basic respiration recap tutorial



Respiration Videos



ATP - The energy currency of the cell

From Wiki -Adenosine triphosphate (ATP) is a nucleoside triphosphate used in cells as a coenzyme, often called the "molecular unit of currency" of intracellular energy transfer.

ATP transports chemical energy within cells for metabolism. It is one of the end products of photophosphorylation, cellular respiration, and fermentation and used by enzymes and structural proteins in many cellular processes

Cell division (DNA replication and mitosis as part of the cell cycle)

A great video by LearnCOACH

DNA Replication

The purpose of DNA replication is to produce two identical copies of a DNA molecule. This is essential for cell division during growth or repair of damaged tissues.

An excellent starter animation can be found here

2013 DNA replication is where the DNA in the cell makes an exact copy of itself prior to cell division so that there is a full set of genetic information available in each cell after division has occurred. 

2014 DNA replication allows cell division to occur because all cells must replicate their DNA before division, so that each new daughter cell has the identical genetic material to the parent cell, so it can function correctly and reproduce. 

DNA replication process (from the exam so this is the detail they were looking for):

An enzyme separates the DNA double helix. Free nucleotide bases A T G C match the exposed bases using the complementary base pairing rule, ie A-T and G-C. Each new helix has one parent strand and one new strand (semi-conservative).



Why is it called semi conservative?


Semi-conservative replication is so named because each molecule of DNA that is created contains one new strand and one old strand.

(You may answer with the etymology of the words; semi = partial, conservative = keeping.)

Process of replication


(Names of enzymes are not necessary but may aid judgement of your understanding , this means for Excellence it will help to know them!)

  • The two strands separate, exposing the bases (unwound by the enzyme helicase), which will act as the template. 
  • Two new polynucleotide chains are formed using the bases of the existing strands as a complementary template. (Carried out by DNA polymerase).
  • Nucleotides join up following the base-pairing rule A-T and C-G.
  • DNA polymerase can only add nucleotides to an existing polynucleotide strand. This is in the form of an RNA primer. (A short length of RNA).
  • Nucleotides can only be added at the 3’ end of a polynucleotide chain.
  • Leading strand can therefore be copied directly, but the lagging strand has to be built in sections (Okazaki fragments) that are then joined together.
A good DNA replication PowerPoint can be found by clicking here.


Mitosis


(Definition and process from 2014 Exam) Mitosis is to replicate genetically identical cells for growth / repair / same function as parent cell in body (somatic) cells.

Process – replicated chromosomes separate, 2 new nuclei form, cell splits in two.

Cells divide for growth, repair, regeneration, asexual reproduction.

Cell division occurs when the distance between the cell membrane and centre of cell becomes so large that substances cannot diffuse fast enough to carry out cell processes. Therefore cells divide to have a high surface-to-volume ratio. This enables efficient chemical reactions.

Mitosis occurs during periods of growth and repair during infancy / childhood / early development in animals following the breaking of dormancy, and during seasonal growth in plants following damage to the organism when repair of tissue is necessary.

Cells will divide by mitosis when growth or replacement of cells needs to occur. This is determined by factors such as cell type / function, For example skin cells are programmed to divide more than brain cells.

Examples of cell types that divide often include, (but are not limited to) root cells, shoot tips, hair follicles, bone marrow, skin cells and mucous membranes. Cells that divide less often include Liver cells and Neurones.


Mitosis Notes Click here

DNA replication interactive animation


A good basic explanation (animation) click here

What is Mitosis? - Quite complicated.

Clicking through the steps

Mitosis Bozeman - worth the watch

What can affect mitosis and the speed it occurs at?

The following can slow down mitosis: temperature, pH, presence of mutagens such as alcohol or radiation, availability of raw materials in the cell.

Mitosis is usually higher during periods of growth and repair during infancy / childhood / early development in animals following the breaking of dormancy, and during seasonal growth in plants following damage to the organism when repair of tissue is necessary.

Mitosis occurs at a higher rate in areas where most growth or replacement of cells is occurring, such as:

·  root / shoot tips

·  hair follicles

·  bone marrow

·  skin cells

·  mucous membranes etc.

Mitosis rates increase in areas of cellular repair, the site of damage. Mitosis rates increase in Cancer cells.


The Cell Cycle


A good animation can be found here

The stages in the cell cycle, are interphase (G1, S, G2, mitosis and cytokenisis) You do not need to know the names!
Interphase: Divided into 3 phases; Gap Phase 1 (Cell grows larger), Synthesis (Genome is replicated, Gap Phase 2 (seperates the newly replicated genome.
Mitosis: Include four stages (prophase, metaphase, anaphase, telophase). Spindle fibers attach to the chromosomes and pull sister chromatids apart. It seperates two daughter genomes.
Cytokinesis: Division of the cytoplasm to form two new cells.

State that interphase is an active period in life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts.

Interphase is an active period in the life of a cell during which many metabolic reactions occur such as protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplast.

Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase)
Prophase: The spindle microtubules are extended from each pole to the equator.
Metaphase: Chromatids move to the equator and the spindle microtubules from each pole attach to each centromere on opposite sides.
Anaphase: spindle microtubules pull sister chromatids apart making the centromeres to split. This brings the sister chromatids apart, splitting them into chromosomes. Each identical chromosome is pulled to opposite poles.
Telophase: Spindle microtubules break down, while chromosomes uncoil and therefore are no longer individually visible. The nuclear membrane now reforms. The cell then is divided by cytokinesis to form two daughter cells with identical genetic nuclei.

Biological ideas, as they relate to each of the life processes at the cellular level



Movement of materials (including diffusion, osmosis, active transport)

A great LearnCOACH video

A starter PowerPoint can be found here

Thanks to biofactor for the following links (:

Cellular transport - Pretty decent overview. Covers cell membrane structure, passive transport (diffusion, osmosis) and active transport.
Membrane transport - Pretty decent overview. Covers cell membrane structure, passive transport (diffusion, facilitated diffusion, osmosis) and active transport (ion pumps, cotransport, endocytosis)
BBC Biology:Investigating cells: Cells and diffusion - Cell structure, diffusion and osmosis.


Diffusion

Diffusion is the spread of particles through random motion from regions of higher concentration to regions of lower concentration until they are equal.




Passive transport - Simple and facilitated diffusion, animated and narrated if you want.
Diffusion: is the passive movement of particles from a region of higher concentration to a region of lower concentration, as a result of the random motion of particles.
Tim and Moby diffusion Click here
How diffusion works - Narrated animation and a short quiz 

Osmosis and Tonicity


Osmosis is the movement of water across a partially (semi) permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration) until they are equal.
How osmosis works - Narrated animation and a short quiz.

Excellent animation

Wikipedia (yes its ok to use!) Link

An animation and quiz. Link

Now watch the following video.

Tonicity is a measure of the relative concentration of solute particles on either side of a semi-permeable membrane (e.g. inside a cell versus outside the cell).

Active transport


Excellent link animation

Active transport - Detailed examples used to explain principles of primary (Na+ / K+ pump) and secondary active transport at a membrane level 
Spoken animation here

Active transport is diffusion that is "facilitated" by proteins that span the membrane and provide an alternative route or bypass. It is similar to simple diffusion in the sense that it does not require expenditure of metabolic energy and transport is again down an electrochemical gradient. Two major groups of integral membrane proteins are involved in facilitated diffusion:

1. Carrier proteins (also known as permeases or transporters) bind a specific type of solute and are thereby induced to undergo a series of conformational changes which has the effect of carrying the solute to the other side of the membrane. The carrier then discharges the solute and, through another conformational change, reorients in the membrane to its original state. Typically, a given carrier will transport only a small group of related molecules.

2. Ion Channels do not really bind the solute, but are like hydrophilic pores through the membrane that open and allow certain types of solutes, usually inorganic ions, to pass through. In general, channels are quite specific for the type of solute they will transport and transport through channels is quite a bit faster than by carrier proteins. Additionally, many channels contain a "gate" which is functions to control the channel's permeability. When the gate is open, the channel transports, and when the gate is closed, the channel is closed. Such gates can be controlled either by voltage across the membrane (voltage-gated channels) or have a binding site for a ligand which, when bound, causes the channels to open (ligand-gated channels). Ion channels allow currents to be carried across the membrane and are thus of particular importance in the physiology of excitable cells like neurons and muscle cells.


Enzyme activity

(specific names of enzymes are not required)

A great video from LearnCoach


What is an enzyme? a good introduction
  • Enzymes are biological catalysts that speed up the rate of reactions or allow reactions to take place in conditions where it would not otherwise be possible.
  • Enzymes are biological catalysts. There are about 40,000 different enzymes in human cells, each controlling a different chemical reaction. They increase the rate of reactions by a factor of between 106 to 1012 times, allowing the chemical reactions that make life possible to take place at normal temperatures. They were discovered in fermenting yeast in 1900 by Buchner, and the name enzyme means "in yeast". As well as catalysing all the metabolic reactions of cells (such as respiration, photosynthesis and digestion), they also act as motors, membrane pumps and receptors.
  • A great website that explains these well can be found here and a NZ resource here.

Enzymes

An excellent powerpoint about enzymes here and another here

Animation 


Factors affecting the processes inside the cell


Availability of energy and materials


Cell division requires energy, enzymes and certain molecules, e.g. nucleotides, proteins (enzymes) The cell must prepare for each division by ensuring that these requirements are stored and available when needed.

Temperature



Enzymes function in specific conditions. Outside of these conditions the enzymes will not function as well.

A temperature that is too low means that substrate / enzyme collisions and interaction will be lower and therefore so will the rate of photosynthesis. As heat increases, there will be an optimum temperature for the functioning of the enzymes associated with photosynthesis in that particular plant. This will be the temperature at which the peak rate of photosynthesis occurs. Beyond (above) this temperature, the enzymes may become denatured which makes them inactive. This latter reaction is irreversible.

They are denatured because of a change in the shape / structure of the active site, which can no longer fit the substrate(s) involved in the process. Once the active site begins to distort, the rate of photosynthesis will decrease, as not as many interactions will be able to take place. If the enzymes become denatured, the rate of photosynthesis would decrease rapidly, and may stop altogether.

details of the processes only as they relate to the overall functioning of the cell (specific names of stages are not required) 

Location of the cell in the organism


Mitosis occurs at a higher rate in areas where most growth, repair and replacement of cells is occurring, e.g. skin, hair follicles, bone marrow, root and shoot tips.


Environmental conditions


Mitosis and DNA replication involve enzymes so that the speed at which these processes take place is affected by factors that affect enzymes, such as temperature and pH.
The presence of mutagens such as alcohol and radiation changes the rate of cell division – rate increases in cancer cells


Reasons for similarities and differences between cells such as cell size and shape, and type and number of organelles present.


•Molecules quickly reach the centre of a small cell.
•Plant cells have a fluid-filled vacuole in the centre of the cell- materials such as oxygen need for life processes, quickly diffuse into organelles around the outside of the vacuole.
How Cells Get Around the SA/V Problem

Subpages (1): Cells Key Words
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