Ch 7: Cells

Question 1

What are all living things made of?

Answer 1

all living things are made of cells. A cell is considered the basic unit of life

Question 2

What are some features of cells?

Answer 2

• are an easily recognised package
• are surrounded by a membrane
• have a highly organised structure with many chemical processes and reactions occurring within
• are able to sense and respond to changes in their environment
• arise from pre-existing cells

Question 3

Convert a metre to centimetres, millimetres, micrometres and nanometres. Then express each unit as a fraction of a metre

Answer 3

Question 4

List the general lengths/diameters of a:

• plant cell
• human red blood cell
• green alga (Chlamydomonas)
• protozoan (Trypanosoma)
• T4 bacteriophage
• AIDS virus
• polio virus
• Escherichia coli (bacterium)
• tobacco mosaic virus

Answer 4

Question 5

What are the features of a light microscope v a electron microscope?

Answer 5

Light microscope

• Light rays from a source beneath the stage are transmitted through two glass lenses in series: the objective and ocular lenses
• Light microscope may magnify 400 times
• Fine structures will not be visible

Electron microscope

• Electron microscopes uses focused beam of electrons and achieves higher magnification
• transmission electron microscope (TEM): the electrons pass through the specimen. The TEM is the most common form of electron microscope and has the best resolution. It can magnify up to 1 500 000 times.
• scanning electron microscope (SEM): solid specimens are bombarded with a beam of electrons, which causes secondary electrons to be emitted from the surface layers of the specimen. The SEM has poorer resolution, but gives excellent 3-dimensional images of surfaces.

Question 6

What are features of prokaryotic cells?

Answer 6

• very small, 1–10 µm in length and 0.2–2.0 µm in diameter
• Simple internal structure - no membrane bound organelles
• Cytoplasm is made up of cytosol fluid together with cell organelles.
• Ribosomes build up (synthesise) proteins from amino acids
• Genetic material in circular chromosome come in direct contact with the cytoplasm – no nuclear membrane. Carry instructions for protein synthesis
• Numerous small rings of DNA, called plasmids
• experience difficulty performing several diferent functions at the same time
• 2 Domains: Bacteria and Archaea

Question 7

What are features of eukaryotes?

Answer 7

• Size 10–100mm in length and 0.2–2.0mm in diameter.
• Membrane-bound organelles - enable cell to carry out multiple different reactions at the same time, important when reactions are incompatible
• Cytoplasm is made up of cytosol fluid and cell organelles
• Ribosomes build (synthesise) proteins from amino acids
• Sarcoplasmic reticulum is where protein is modified and transported
• Membrane-bound nucleus contains DNA
• Organelles also separate chemical reactions in time i.e. when substances are stored and then used in other reactions. Also facilitate the synthesis of complex molecules

Question 8

What does a eukaryotic animal cell look like?

Answer 8

Question 9

What does a eukaryotic plant cell look like?

Answer 9

Question 10

What are the features of the nucleus?

Answer 10

• one of the most prominent organelles in a eukaryotic cell - clearly visible under light or electron microscope
• control centre of the cell - by coding for different proteins at different times and in different cells the nucleus can coordinate the activities of the cell
• main molecule inside is DNA (bundled chromosomes that code for the production of proteins that carry out a variety of activities)
  
  • chromosomes - rod shaped and surronded by a membrane which keeps the DNA separate from the chemical reactions of the cytoplasm making it easier for DNA to be copied and organised before cell division

Question 11

What are the unspecialised cells in our body?

Answer 11

Most of the cells of our body (e.g. blood, liver, brain and nerve cells) are specialised to perform particular functions. Stem cells are unspecialised cells that have the potential to develop into many different kinds of cell. Unlike most specialised cells, they also have the capacity to keep dividing.

Question 12

What is photosynthesis and where does it occur?

Answer 12

Photosynthesis is a series of reactions that occur in the stroma and thylakoid membrane system of the chloroplast.

During these photosynthesis reactions carbon dioxide and water are combined to produce glucose, oxygen and water.

Question 13

What aids in allowing a greater amount of photosynthesis reactions to occur?

Answer 13

The internal membranes of a chloroplast are folded many times, this provides more sureface area for chemical reactions of photosynthesis to occur

Question 14

What is cellular respiration

Answer 14

Cellular respiration is a series of chemical reactions that involve a reaction between glucose and oxygen to produce carbon dioxide and water. During certain stages of these chemical reactions energy is released and this is used to build up molecules of adenosine triphosphate (ATP).

In eukaryotic cells, the first stage of cellular respiration takes place in the cytoplasm. The final stage occurs in mitochondria.

Question 15

What are features of mitochondria and how does it aid cellular respiration?

Answer 15

• small, oval-shaped structures found scattered throughout the cytosol of a cell.
• each mitochondrion consists of an outer smooth membrane and a highly folded inner membrane (cristae). The folds in the inner membrane protrude into the inner space of the mitochondrion, a protein-rich fluid called the matrix.
• these cristae provide two important features to cellular respiration:
  
  • The enzymes for cellular respiration are located mainly on the cristae.
  • The numerous folds of the cristae provide a large surface area for the chemical reactions to occur.

Question 16

What is the endosymbiosis theory?

Answer 16

proposes that eukaryote cells were formed when a bacterial cell was ingested by another primitive prokaryotic cell.

Question 17

Why do cells need biomacromolecules and how are they grouped?

Answer 17

Every living cell is involved in synthesising these large molecules that are needed not only to build the body parts of organisms but also to maintain the biochemical processes that keep them living: communication, transforming energy and relaying genetic information.

grouped into four main classes based on their chemical composition and structure

• complex carbohydrates
• lipids
• proteins
• nucleic acids

Question 18

What is a carbohydrate and what are features of carbohydrates?

Answer 18

>organic compound that serves as a structural component and a major energy sourc in the diet of animals : includes sugars, starches, celulloses and gums

• each molecule consists of carbon, hydrogen and oxygen atoms in the ratio of 1:2:1, giving the general formula for carbohydrates as nCH2O
• carbohydrates are classified into:
  
  • monosaccharides - simple sugar which cannot be broken down into smaller sugar molecules i.e. glucose
  • disaccharides - 2 linkes monosaccharides i.e. sucrose (glucos +fructose)
  • polysaccharides - complec carbohydrates that are made up by linking together simple sugars i.e. cellulose

Question 19

What is a lipid and what are some features?

Answer 19

>organic molecule insoluble in water, diverse group of molecules and include fats and oils, terpenes, waxes, phospholipids, glycolipids and steroids.

• Lipids all contain the elements carbon, hydrogen and oxygen
• oils + fats in plants and animals typically composed of triglyceride molecules (fatty acid chains + glycerol molecules)

Important functions:

1. energy storage (they have approximately twice the amount of energy as carbohydrates)
2. structural component of membranes
3. specific biological functions (e.g. transmission of chemical signals both within and between cells).

• cells also excret lipids that function to protect the cell/organism to which it belongs

Question 20

What are proteins and what are some features?

Answer 20

>large organic molecule, built up from amino acids, made up of the elements carbon, hydrogen and oxygen, always contain nitrogen. Also often contain sulfur, phosporous or other elements

• Amino acids are made into proteins in the ribosomes.
• Plants can synthesise their own amino acids.
• Amino acids are linked by peptide bonds to form a polypeptide chain.
• The order of amino acids is determined by the genes in our chromosomes.
• Polypeptide chains folds to give each protein its characteristic features.
• Mammals use 20 amino acids to make proteins +2 ‘non standard’ amino acids
• 9 essential amino acids must be taken from our diet (can’t be synthesised in cells)

Question 21

What is the importance of proteins?

Answer 21

>Virtually everything a cell is, or does, depends on the proteins it contains.

• They contribute to building many different structures and parts
• and, as enzymes, control the thousands of chemical reactions that maintain life processes.

Question 22

What is nucleic acid and what are its features?

Answer 22

>large organic molecule made up of nucleotides

• main function: cells carry out many and varied tasks, usually at the same time. To be an efficient system a cell needs to have some way of coordinating all of these activities.
• The nucleic acids DNA and RNA are found in the nucleus.

Question 23

What is DNA?

Answer 23

• A molecule of DNA is composed of two long strands of sub-units called nucleotides. They are wound around each other to form a double helix.
• codes for the production of proteins that carry out and control the many activities within a cell. When a cell divides, new DNA is synthesised.
• Each DNA molecule is large. They are too large to move through the nuclear membrane. It is the job of messenger RNA (mRNA) to transfer the DNA code to the ribosomes for protein synthesis. The order of nucleotides in mRNA is determined by the order of nucleotides in a section of DNA.
• After synthesis of a strand of mRNA has been completed, it moves from the nucleus to ribosomes in the cytoplasm. The order of nucleotides in the mRNA determines the order of amino acids in protein synthesis.

Question 24

What is endoplasmic reticulum?

Answer 24

> Interconnecting membrane sheets dividing the cytoplasm into compartments.

• Membrane produces vesicles to transport proteins within and between cells.
• Rough ER: studded with ribosomes so protein can enter the ER directly, transports proteins that are synthesised in the ribosomes
• Smooth ER: is where specialised lipids are synthesised.
• Major calcium store.

Question 25

What are the golgi apparatus?

Answer 25

> stack of membrane bound flattened sacs

• modification/packaging of proteins received from the ER. These proetins are then transported in vesicles around the cells/out of the cell

1. Proteins produced by ribosomes are stored in the rough ER.
2. Transported by vesicles to Golgi apparatus.
3. Finishing touches given to protein by enzymes then stored in vesicles.
4. Vesicles bud off the Golgi apparatus and transport contents to cell membrane.
5. Contents discharged by exocytosis.
6. Lysosomes contain enzymes that breakdown and recycle organelles or damaged macromolecules.

Question 26

What are lysosomes?

Answer 26

> an organelle within the cytoplasm containing digestive enzymes

• recycles raw materials of organelles by breaking it down to simpler compounds which can be used as building blocks for new compounds
• destroys entire cells - apoptosis - by rupturing membrane, releasing the enzymes, which then digest the contents of the cell

Question 27

What is the plasma membrane and how are large molecules able to move across the membrane?

Answer 27

> selectivley allows substances to pass through

• to allow large molecules to move across the membrane enodcytosis and exocytosis are used

Question 28

What is endo/exo - cytosis?

Answer 28

exocytosis: a small membrane bound vesicle moves to the cytoplasm to the membrane where it joins with it and releases its contents to the exterior of the cell
endocytosis: plasma membrane engulfs the material within it to form an endocytic vesicle which then stores and transports the materials within the cytoplasm