Topic 1: Cells

1.1 Cell Theory Discuss the theory that living organisms are composed of cells. (3) Skeletal muscle and some fungal hyphae are not divided into cells but have a multinucleate cytoplasm. Some biologists consider unicellular organisms to be acellular.

1.1 Cell Theory State that a virus is a non-cellular structure consisting of DNA or RNA surrounded by a protein coat. (1)

1.1 Cell Theory

1.1.3 State that all cells are formed from other cells. (1) xref Mitosis, 8.1- Meiosis xref Mitosis, 8.1- Meiosis

1.1 Cell Theory Explain three advantages of using light microscopes. (3) Advantages include: colour images instead of monochrome, colour images instead of monochrome, a larger field of view, a larger field of view, easily prepared sample material, easily prepared sample material, the possibility of examining living material and observing movement. the possibility of examining living material and observing movement.

1.1 Cell Theory Outline the advantages of using electron microscopes. (2) Greater: Resolution – the ability to distinguish between two points on an image. Like pixels in a digital camera. Magnification – how much bigger a sample appears to be under the microscope than it is in real life.

1.1 Cell Theory Transmission electron microscopes pass a beam of electrons through the specimen. The electrons that pass through the specimen are detected on a fluorescent screen on which the image is displayed. Thin sections of specimen are needed for transmission electron microscopy as the electrons have to pass through the specimen for the image to be produced.

1.1 Cell Theory Scanning electron microscopes pass a beam of electrons over the surface of the specimen in the form of a ‘scanning’ beam. Scanning electron microscopes pass a beam of electrons over the surface of the specimen in the form of a ‘scanning’ beam. Electrons are reflected off the surface of the specimen as it has been previously coated in heavy metals. Electrons are reflected off the surface of the specimen as it has been previously coated in heavy metals. It is these reflected electron beams that are focused on the fluorescent screen in order to make up the image. It is these reflected electron beams that are focused on the fluorescent screen in order to make up the image. Larger, thicker structures can thus be seen under the scanning electron microscope as the electrons do not have to pass through the sample in order to form the image. Larger, thicker structures can thus be seen under the scanning electron microscope as the electrons do not have to pass through the sample in order to form the image. However the resolution of the scanning electron microscope is lower than that of the transmission electron microscope. However the resolution of the scanning electron microscope is lower than that of the transmission electron microscope.

1.1 Cell Theory LightElectron Cheap to purchase (£100 – 500) Expensive to buy (over £1,000,000) Cheap to operate Expensive to produce electron beams Small and portable Large and requires special rooms Simple and easy preparations Lengthy and complex preparations Material rarely distorted by preparation Preparation distorts material Vacuum is not required Vacuum is required Natural color maintained All images in black and white Magnifies objects only up to 2000 times Magnifies over 500,000 times

1.1 Cell Theory Define organelle. (1) Literally ‘little organ’ Literally ‘little organ’ An organelle is a discrete structure within a cell, and has a specific function. An organelle is a discrete structure within a cell, and has a specific function. i.e. – nucleus, cell membrane, mitochondria

1.1 Cell Theory Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using appropriate SI units (2) Appreciation of relative size is required, molecules (1 nm), molecules (1 nm), thickness of membranes (10 nm), xref. 1.4 thickness of membranes (10 nm), xref. 1.4 viruses (100 nm), viruses (100 nm), bacteria (1 µm), xref bacteria (1 µm), xref organelles (up to 10 µm), xref , 7.1.3, organelles (up to 10 µm), xref , 7.1.3, most cells (up to 100 µm). most cells (up to 100 µm). Don’t forget: all of these structures are in 3D space

1.1 Cell Theory 1 nm = 1/1,000,000,000 of a meter, or m, or m, or... 1 billionth of a meter 1 billionth of a meter 1 µm = 1/1,000,000 of a meter, or m, or m, or... 1 millionth of a meter 1 millionth of a meter 1 nm = 1/1,000 of a µm, or 1 µm = 1,000 nanometers Therefore...

1.1 Cell Theory A 100 µm cell 10x larger than a... A 10 µm organelle10x larger than a... A 1 µm bacteria10x larger than a... A 100 nm virus10x larger than a... A 10 nm membrane 10x larger than a... A 1 nm molecule

1.1 Cell Theory

1.1.8 Calculate linear magnification of drawings. (2) Drawings should show cells and cell ultra-structure with scale bars Magnification could also be stated, eg x250.

1.1 Cell Theory Explain the importance of the surface area to volume ratio as a factor limiting cell size. (3) The rate of metabolism of a cell is a function of its mass:volume ratio, Whereas the rate of exchange of materials and energy (heat) is a function of its surface area. Simple mathematical models involving cubes and the changes in the ratio that occur as the sides increase by one unit could be compared.

cm 10 cm 100 cm Assume we have 3 cubes: With sizes: What will happen to ratio between V and S.A. as their size increases?

Ratio of V:S.A. Cube Side Length Volume (x 3 ) S.A. (6x 2 ) Ratio (S.A./V) 1 1 cm 2 10 cm cm 1 cm cm cm 3 6 cm cm cm

1.1 Cell Theory State that unicellular organisms carry out all the functions of life. (1) MOVEMENT – Intracellular and/or extracellular RESPIRATION – Gas exchange. Not always O 2 and CO 2 NUTRITION – Need raw materials, i.e.- food, water, minerals EXCRETION – Get rid of waste materials REPRODUCTION – Ability to produce like organisms IRRATIBILITY – Respond to external stimuli GROWTH – Cells grow larger... and don’t forget... ‘MR. NERIG’ also carries out the functions of life!

1.1 Cell Theory Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others. (3)

1.1 Cell Theory Define: (1) Tissue – A group of cells working together to perform a common function Organ – A group of tissues working together to perform a common function Organ System – A group of organs working together to perform a common function

1.2 Prokaryotic Cells Draw a generalized prokaryotic cell as seen in electron micrographs. (1) Use images of bacteria as seen in electron micrographs to show the structure. Use images of bacteria as seen in electron micrographs to show the structure. The diagram should show the cell wall, plasma membrane, mesosome, cytoplasm, ribosomes and nucleoid (region containing naked DNA). The diagram should show the cell wall, plasma membrane, mesosome, cytoplasm, ribosomes and nucleoid (region containing naked DNA).

1.2 Prokaryotic Cells State one function for each of the following: (1) cell wall – forms a protective outer layer that prevents damage from outside and bursting if internal pressure is too high cell wall – forms a protective outer layer that prevents damage from outside and bursting if internal pressure is too high plasma membrane – controls entry and exit of substances, pumping some of them in by active transport plasma membrane – controls entry and exit of substances, pumping some of them in by active transport

1.2 Prokaryotic Cells mesosome – increases the area of membrane for ATP production. May move the DNA to the poles during cell division mesosome – increases the area of membrane for ATP production. May move the DNA to the poles during cell division cytoplasm – contains enzymes that catalyse the chemical reactions of meabolism and DNA in a region call the nucleoid cytoplasm – contains enzymes that catalyse the chemical reactions of meabolism and DNA in a region call the nucleoid

1.2 Prokaryotic Cells ribosomes – synthesize proteins by translating messenger RNA. Some proteins stay in the cell and others are secreted ribosomes – synthesize proteins by translating messenger RNA. Some proteins stay in the cell and others are secreted naked DNA – stores the genetic information that controls the cell and is passed on to daughter cells naked DNA – stores the genetic information that controls the cell and is passed on to daughter cells

1.2 Prokaryotic Cells State that prokaryotes show a wide range of metabolic activity including fermentation, photosynthesis and nitrogen fixation. (1)

1.3 Eukaryotic Cells Draw a diagram to show the ultrastructure of a generalized animal cell as seen in electron micrographs. (1) The diagram should show ribosomes, rough endoplasmic reticulum (rER), lysosome, Golgi apparatus, mitochondrion and nucleus. The diagram should show ribosomes, rough endoplasmic reticulum (rER), lysosome, Golgi apparatus, mitochondrion and nucleus.

Insert electron micrograph and diagram of eukaryotic cells

1.3 Eukaryotic Cells 1.3 Eukaryotic Cells State one function of each of these organelles: (1) ribosomes – protein synthesis rough endoplasmic reticulum (rER) – synthesis of proteins to be secreted lysosome – holds digestive enzymes Golgi apparatus – for processing of proteins mitochondrion – for aerobic respiration nucleus – holds the chromosomes

1.3 Eukaryotic Cells 1.3.3Compare prokaryotic and eukaryotic cells: (2) Differences should include: naked DNA in a loop versus DNA associated with protein in strands, naked DNA in a loop versus DNA associated with protein in strands, DNA in cytoplasm versus DNA enclosed in a nuclear envelope, DNA in cytoplasm versus DNA enclosed in a nuclear envelope, no mitochondria versus mitochondria, no mitochondria versus mitochondria, 70S versus 80S ribosomes. 70S versus 80S ribosomes. Similarities include: Both types have cell membranes, cytoplasm, DNA and ribosomes (although slightly different) Both types have cell membranes, cytoplasm, DNA and ribosomes (although slightly different)

1.3 Eukaryotic Cells Describe three differences between plant and animal cells.(2) Carbohydrates stored as starch. Carbohydrates stored as glycogen. Stores large amounts of liquid (juice). Larger size of cell.  Central Vacuole XDoes not store large amounts of liquid. Smaller size of cell. Rigid, cannot easily change shape.  Cell Wall XFlexible, can easily change shape. Can produce its own food. ChloroplastXCannot produce its own food Plant Cells Structure Animal Cells

1.3 Eukaryotic Cells State the composition and function of the plant cell wall. (1) The composition of the plant cell wall should be considered only in terms of cellulose microfibrils. The composition of the plant cell wall should be considered only in terms of cellulose microfibrils.

1.4 Membranes Draw a diagram to show the fluid mosaic model of a biological membrane. (1) The diagram should show the phospholipid bilayer, cholesterol, glycoproteins and integral and peripheral proteins. The diagram should show the phospholipid bilayer, cholesterol, glycoproteins and integral and peripheral proteins. Use the term plasma membrane not cell surface membrane for the membrane surrounding the cytoplasm. Use the term plasma membrane not cell surface membrane for the membrane surrounding the cytoplasm. Integral proteins are embedded in the phospholipid of the membrane whereas peripheral proteins are attached to its surface. Integral proteins are embedded in the phospholipid of the membrane whereas peripheral proteins are attached to its surface.

1.4 Membranes Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes. (3) Hydrophobic – ‘afraid of water’ Hydrophilic – ‘loves water’

1.4 Membranes

Plasma Membranes

1.4 Membranes List the functions of membrane proteins including (1) hormone binding sites hormone binding sites enzymes enzymes electron carriers electron carriers channels for passive transport channels for passive transport pumps for active transport. pumps for active transport.

1.4 Membranes Define diffusion (1) Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration (down a concentration gradient), until there is an equal distribution. Define osmosis Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration (high water concentration) to a region of higher solute concentration (low water concentration).

1.4 Membranes High Concentration Low Concentration Diffusion moves down the concentration gradient just like a ball rolling down a hill. It cannot roll uphill without energy.

1.4 Membranes Explain passive transport across membranes in terms of diffusion.(3) Requires no energy Moves from down the concentration gradient Some molecules pass through the membrane Some molecules use channels for facilitated diffusion

1.4 Membranes

1.4.6 Explain the role of protein pumps and ATP in active transport across membranes.(3) Requires energy, in the form of ATP, or adenosine triphosphate Molecules are ‘pumped’ across the membrane UP the concentration gradient Pumps fit specific molecules The pump changes shape when ATP activates it, this moves the molecule across the membrane

Active Transport

1.4 Membranes Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane. (3) 1.4.8Describe how the fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis. (2)

1.4 Membranes Endocytosis – the mass movement INTO the cell by the membrane ‘pinching’ into a vacuole Exocytosis – the mass movement OUT of the cell by the fusion of a vacuole and the membrane This is possible because the of the fluid properties of the membrane (able to break and reform easily, phospholipids not attached just attracted)

Exocytosis

Endocytosis endo- and exo- -cytosis

1.5 Cell Division State that the cell-division cycle involves interphase, mitosis, and cytokinesis. (1) Interphase Mitosis Cytokinesis

1.5 Cell Division State that interphase is an active period in the life of a cell when many biochemical reactions occur, as well as DNA transcription and DNA replication. (1)

1.5 Cell Division Describe the events that occur in the four phases of mitosis (2)

1.5 Cell Division PROPHASE - breakage of nuclear membranes and supercoiling of DNA to form visible chromosomes

1.5 Cell Division METAPHASE - chromosomes line up along equatorial region of cell, attachment of spindle microtubules to centromeres

1.5 Cell Division ANAPHASE - splitting of centromeres, movement of sister chromosomes to opposite poles as spindle microtubules shorten

1.5 Cell Division TELOPHASE - uncoiling of chromosomes and reformation of nuclear membranes

1.5 Cell Division P rophase M etaphase A naphase T elophase P-MAT

Drosophilia Embryo Division Mitosis Video

1.5 Cell Division 1.5.4Explain how mitosis produces two genetically identical nuclei.(3) Synthesis of identical chromosomes in interphase Lining up during mitosis ensures that each new cell gets a copy of each chromosome

1.5 Cell Division Outline the differences in mitosis and cytokinesis between animal and plant cells.(2) No centrioles in plant cells Cell plate formed in plants, membrane ‘pinching’ in animal cells Cytokinesis

1.5 Cell Division

1.5.6 State that growth, tissue repair and asexual reproduction involve mitosis.(1) State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ. (1)