IB Biology HL Unit 1 essay questions w/ markscheme
Eukaryotic cells have intracellular and extracellular components. State the functions of one named extracellular component. 4 marks
name of component: 1 max e.g. plant cell wall/cellulose/interstitial functions: 3 max e.g. (plant cell wall) strengthens/supports the cell/plant (against gravity); -prevents the entry of pathogens; -maintains the shape of plant cells; -allows turgor pressure/high pressure to develop inside the cell; -prevents excessive entry of water to the cell Matrix: -helps cells to stick together/adhere; -needed to hold cells/tissues together / example of cells/tissues holding together; -forms interstitial matrix / forms basement membrane to support single layers of cells; -e.g. around a blood capillary; forms (part of the) filtration membrane in the glomerulus;
Draw a labelled diagram to show the organelles which are found in the cytoplasm of plant cells. 6 marks
rough endoplasmic reticulum free ribosomes Golgi apparatus mitochondrion chloroplast vacuole nucleus lysosome smooth endoplasmic reticulum
Using a table, compare the structures of prokaryotic and eukaryotic cells. 5 marks
-DNA: P: naked/loop of DNA; E: associated with protein/histones/nucleosomes/DNA in chromosomes -location of DNA: P: in cytoplasm/nuceloid/no nucleus; E: within a nucleus/nuclear membrane -membrane bound organelles: P: none; E: present -ribosomes: P: 70S ; E: 80S -plasma membrane: P & E: same structure within both groups -cell wall: P: peptidoglycan/not cellulose/not chitin; E: cellusose/chitin/not peptidoglycan -respiratory structures: P: no mitochondria; E: mitochondria -pili: P: pili present E: pili absent; -plasmids: P: plasmids (sometimes) present E:plasmids absent; -flagella: P: flagella solid E: flagella flexible/membrane-bound;
Draw a labelled diagram to show the ultrastructure of Escherichia coli. 6 marks
-cell wall - with some thickness; -plasma membrane - shown as single line or very thin; -cytoplasm; -pilus/pili - shown as single lines; -flagellum/flagella - shown as thicker and longer structures than pili and embedded in cell wall; -70S ribosomes; -nucleoid / naked DNA; -approximate width 0.5 μm / approximate length 2.0 μm;
Outline differentiation of cells in a multicellular organism. 4 marks
-differentiation is development in different/specific ways -cells carry out specialized functions/become specialized -example of a differentiated cell in a multicelluar organism -cells have all genes/could develop in any way -some genes are switched on/expressed but not others -position/hormones/cell-to-cell signals/chemicals determine how a cell develops -a group of differentiated cells is a tissue
Distinguish between the structure of plant and animal cells. 6 marks
-have cell walls, animals do not -have plastids/ chloroplasts, animals do not -have a large central vacuole, animals do not -store starch, animal cells store glycogen -have plasmodesmata, animal cells do not animal cells -have centrioles, plant cells do not -have cholesterol in the cell membrane, plant cells do not -plant cells are generally have a fixed shape/ more regular whereas animal cells are more rounded
State one function of each of the following organelles: lysosome, Golgi apparatus, rough endoplasmic reticulum, nucleus, mitochondrion. 5 marks
-lysosome: hydrolysis/digestion/break down of materials (macromolecules) -Golgi apparatus: synthesis/sorting/transporting/secretion of cell products -rough endoplasmic reticulum: site of synthesis of proteins (to be secreted)/ intracellular transport of polypeptides to Golgi apparatus -nucleus: controls cells activities/mitosis/replication of DNA/transcription of DNA (to RNA)/directs protein synthesis -mitochondrion: (aerobic) respiration/generates ATP
Discuss possible exceptions to cell theory. 4 marks
-skeletal muscle fibers are larger/have many nuclei/are not typical cells -fungal hyphae are (sometimes) not divided up into individual cells -unicellular organisms can be considered acellular because they are larger than a typical cell/carry out all functions of life -some tissues/organs contain large amounts of extracellular material -e.g. vitreous humor of eye/ mineral deposits in bone/ xylem in trees/other example -statement of cell theory/all living things/most tissues are composed entirely of true cells
Explain how the surface are to volume ratio influences cell sizes. 3 marks
-small cells have larger ratio (than larger cells)/ratio decreases as size increases -surface area/membrane must be large enough to absorb nutrients/oxygen/substances needed -surface area/membrane must be large enough to excrete/pass out waste products -need for materials is determined by (cell) volume -cell size is limited (by SA/Volume ratio)/cells divide when they reach a certain size -reference to diffusion across/through membrane/surface area
Describe the importance of stem cells in differentiation. 3 marks
-stem cells are undifferentiated cells; -embryo cells are stem cells; -stem cells can differentiate in many/all ways / are pluripotent/totipotent; -differentiation involves expressing some genes but not others; -stem cells can be used to repair/replace tissues/heal wounds;