Chapter 1.2

Question 1

electron micrograph: animal cells

Answer 1

Question 2

electron micrographs: plant cells

Answer 2

Question 3

The ultrastructure of an animal cell shows a densely packed cell

Answer 3

Question 4

Plant cells diagram

Answer 4

Question 5

Cell surface membrane

Answer 5

-All cells are surrounded by a cell surface membrane which controls the exchange of materials between the internal cell environment and the external environment -The membrane is described as being ‘partially permeable’ -The cell membrane is formed from a phospholipid bilayer of phospholipids spanning a diameter of around 10 nm

Question 6

Cell wall

Answer 6

-Cell walls are formed outside of the cell membrane and offer structural support to cell -Structural support is provided by the polysaccharide cellulose in plants, and peptidoglycan in most bacterial cells -Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells

Question 7

Nucleus

Answer 7

-Present in all eukaryotic cells, the nucleus is relatively large and separated from the cytoplasm by a double membrane (the nuclear envelope) which has many pores -Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes (eg. DNA polymerases) and signalling molecules to travel in -The nucleus contains chromatin (the material from which chromosomes are made) -Usually, at least one or more darkly stained regions can be observed – these regions are individually termed ‘nucleolus’ and are the sites of ribosome production

Question 8

Mitochondria

Answer 8

-The site of aerobic respiration within eukaryotic cells, mitochondria are just visible with a light microscope -Surrounded by double-membrane with the inner membrane folded to form cristae -The matrix formed by the cristae contains enzymes needed for aerobic respiration, producing ATP -Small circular pieces of DNA (mitochondrial DNA) and ribosomes are also found in the matrix (needed for replication)

Question 9

Chloroplast

Answer 9

-Larger than mitochondria, also surrounded by a double-membrane -Membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana -Grana are joined together by lamellae (thin and flat thylakoid membranes) -Chloroplasts are the site of photosynthesis: —-The light-dependent stage takes place in the thylakoids —-The light-independent stage (Calvin Cycle) takes place in the stroma Also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis

Question 10

Ribosome

Answer 10

-Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells -Each ribosome is a complex of ribosomal RNA (rRNA) and proteins -80S ribosomes (composed of 60S and 40S subunits) are found in eukaryotic cells -70S (composed of 50S and 30S subunits) ribosomes in prokaryotes, mitochondria and chloroplasts -Site of translation (protein synthesis)

Question 11

Endoplasmic reticulum

Answer 11

Rough Endoplasmic Reticulum (RER) -Surface covered in ribosomes -Formed from continuous folds of membrane continuous with the nuclear envelope -Processes proteins made by the ribosomes Smooth Endoplasmic Reticulum (ER) -Does not have ribosomes on the surface, its function is distinct to the RER -Involved in the production, processing and storage of lipids, carbohydrates and steroids

Question 12

Golgi apparatus (golgi complex)

Answer 12

-Flattened sacs of membrane similar to the smooth endoplasmic reticulum -Modifies proteins and packages them into vesicles or lysosomes

Question 13

Large permanent vacuole

Answer 13

-Sac in plant cells surrounded by the tonoplast, selectively permeable membrane -Vacuoles in animal cells are not permanent and small

Question 14

Vesicle

Answer 14

Membrane-bound sac for transport and storage

Question 15

Lysosome

Answer 15

-Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break biological molecules down) -Break down waste materials such as worn-out organelles, used extensively by cells of the immune system and in apoptosis (programmed cell death)

Question 16

Centriole

Answer 16

-Hollow fibres made of microtubules, two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division -Not found in flowering plants and fungi

Question 17

Microtubules

Answer 17

-Makes up the cytoskeleton of the cell about 25 nm in diameter -Made of α and β tubulin combined to form dimers, the dimers are then joined into protofilaments. -Thirteen protofilaments in a cylinder make a microtubule -The cytoskeleton is used to provide support and movement of the cell

Question 18

Microvilli

Answer 18

Cell membrane projections that increase the surface area for absorption

Question 19

Cilia

Answer 19

-Hair-like projections made from microtubules -Allows the movement of substances over the cell surface

Question 20

Flagella

Answer 20

-Similar in structure to cilia, made of longer microtubules -Contract to provide cell movement for example in sperm cells

Question 21

Structure of Animal & Plant Cells which are not found in each other

Answer 21

-The only structures found in animal cells but not plant cells are the centrioles and microvilli -Plant cells also have additional structures: the cellulose cell wall, large permanent vacuoles and chloroplasts

Question 22

Prokaryotic cells diagram, whatsa present always and sometimes present

Answer 22

Question 23

The Vital Role of ATP

Answer 23

-All organisms require a constant supply of energy to maintain their cells and stay alive -This energy is required: —-In anabolic reactions – building larger molecules from smaller molecules —-To move substances across the cell membrane (active transport) or to move substances within the cell -In animals, energy is required: —-For muscle contraction – to coordinate movement at the whole-organism level —-In the conduction of nerve impulses, as well as many other cellular processes -In all known forms of life, ATP from respiration is used to transfer energy in all energy-requiring processes in cells -This is why ATP is known as the universal energy currency -Adenosine Triphosphate (ATP) is a nucleotide —-The monomers of DNA and RNA are also nucleotide

Question 24

Structural Features of Typical Prokaryotic Cells

Answer 24

Prokaryotes have a cellular structure distinct from eukaryotes:

• Their genetic material is not packaged within a membrane-bound nucleus and is usually circular (eukaryotic genetic material is packaged as linear chromosomes)
• Prokaryotes lack membrane-bound organelles
• They are many (100s/1000s) of times smaller than eukaryotic cells
• Their ribosomes are structurally smaller (70 S) in comparison to those found in eukaryotic cells (80 S)

Question 25

Prokaryotic & eukaryotic cells comparison table

Answer 25

Question 26

Key Features of Viruses

Answer 26

• Viruses are non-cellular infectious particles that straddle the boundary between ‘living’ and ‘non-living’
• They are relatively simple in structure; much smaller than prokaryotic cells (with diameters between 20 and 300 nm) -Structurally they have: —-A nucleic acid core (their genomes are either DNA or RNA, and can be single or double-stranded)
• A protein coat called a ‘capsid’
• Some viruses have an outer layer called an envelope formed usually from the membrane-phospholipids of a cell they were made in -All viruses are parasitic in that they can only reproduce by infecting living cells and using their protein-building machinery (ribosomes) to produce new viral particles

Question 27

this is just one example of a virus structure

Answer 27