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Structure - Plant Cells

 

	How do prokaryotes and eukaryotes differ in terms of cellular structure and function?
	Eukaryotic cells: membrane-bound organelles chromosomes nuclear membrane Prokaryotic cells: lack a nuclear membrane lack of complex chromosomes known as bacteria

	What do (almost) all of the cells of a (eukaryotic) organism have in common?
	nucleus bounded by a double membrane

	What separates cellular compartments?
	lipid membranes

	What three features make most plant cells different from most animal cells?
	cell wall plastids vacuoles

	Which organelles are bounded by double membranes?
	nucleus plastids mitochondrion

	What are three functions of the plasma membrane?
	uptake of nutrients sensing external stimuli cellulose synthesis

	What does the nucleus contain and what might we be able to see or on it?
	contains DNA, genes, chromosomes nucleolus

	What forms can plastids take and what function do they have?
	chloroplasts - photosynthesis amyloplasts - starch storage chromoplasts - pigmentation

	What do mitochondria do for the cell?
	site of energy release through respiration

	Identify four features or functions of the vacuole.
	osmo-regulation - turgor pressure maintains tissue rigidity storage of products of metabolism breakdown of macromolecules removal of waste products

	What do ribosomes do for the cell?
	site of protein synthesis

	What comprises the endomembrane system and what happens in it?
	endoplasmic reticulum - membrane, molecular traffic, processing dictyosomes (Golgi apparatus - membrane traffic, secretion plasma membrane - cell wall synthesis, signalling, uptake/secretion

	What are the components of the cytoskeleton and what does it do?
	involved in cell division, growth and differentiation, movement of organelles actin filaments involved in cytoplasmic streaming microtubules organize mitosis and cell wall synthesis

	What kinds of material are present in the middle lamella, a microfibril and the primary wall matrix?
	middle lamella consist of pectin providing cell adhesion microfibril contain cellulose (glucose polymer) primary wall matrix consist of hemicellulose and pectin

	How does secondary wall differ from primary wall?
	secondary wall has a higher proportion of cellulose and hemicellulose secondary wall is often lignified

	What is happening to the chromosomes during G1, S and G2 phases?
	G1(gap) phase - starts with a single copy and occurs after mitosis; the cell increases in size S(synthesis) phase - DNA synthesis G2 phase - double copy; transcription of DNA to RNA throughout interphase

	Which parts of the cell contain DNA?
	nucleus plastid mitochondria

	How do we know the functions of mitochondria, plastids etc.?
	mostly because biochemists have isolated organelles and studied their reactions

	Where in the plant do parenchyma cells occur- do they occur on their own or with other cell types?
	both on their own and mixed with other cell types as "ground tissue"

	Distinguish between parenchyma, collenchyma and sclerenchyma.
	Parenchyma has thin primary walls Collenchyma has thick walls Sclerenchyma has thick secondary walls

	Apart from water conduction, what are other functions of zylem?
	strength and storage (in xylem parenchyma)

	What is the difference between tracheids and vessels?
	tracheids are thin with end walls vessel elements are wide and have lost most of their end walls

	What are their advantages and disadvantages for water conduction?
	Vessels allow rapid water movement, but can easily get blocked by air bubbles.

	What other cell types occur in zylem?
	fibers and parenchyma

	What cellular structures would you expect to see inside mature tracheids or vessels?
	none

	What feature of the phloem suggests that food-conduction might be different from water conduction in the xylem?
	Sieve elements contain living cytoplasm.

	What structures found in typical cells are missing from sieve tube members?
	nuclei

	What do you think a companion cell might do for a sieve tube member?
	help it stay alive.

	How do the ends of sieve tube members differ from those of tracheary elements?
	sieve plate present

	Is the epidermis always the outermost layer of cells?
	in young, non-woody parts (often lost in older woody parts)

	What are two major differences between most leaf epidermal cells and most of the cells inside the leaf?
	no chloroplasts inside and no intercellular spaces between epidermal ground cells

	Which leaf epidermal cells do not show one of these differences?
	guard cells have chloroplasts

	How might the presence of trichomes help plant conserve water.
	slow down air movement at leaf surface

	How would you expect root epidermis to differ from leaf epidermis?
	little or no cuticle no stomata presence of root hairs

	What happens in the first meiotic prophase which is different from prophase in mitosis?
	Pairs of homologous chromosomes from parental sets come together.

	What part of a lipid molecule is in the middle of a lipid bilayer? glycerol phosphate fatty acid
	Glycerol links the two ends of the lipid molecule (hydrophilic "head" and hydrophobic "tail"). It is towards the edge of the membrane.   Phosphate (if present) is part of the hydrophilic head group on the outside of the membrane, close to water.   Oil and water don't mix, so the fatty acid "tails" are always towards the center of the lipid bilayer.

	What kind of movement of molecules (plant nutrients, pesticides etc.) would occur across a simple lipid bilayer? passive diffusion active transport none
	Yes, depending on molecular weight and solubility in the lipid phase molecules would slowly diffuse across the membrane.   This would require energy and there is nothing in a simple bilayer to provide it.   Membranes are "semi-permeable" so that molecules always tend to move across them to some extent.

	Specific features of plant cells include: mitochondria, nucleus and ribosomes plasmamembrane, Golgi and ER tonoplast, plastids and cellulose
	These are not specific to plants: they are found in all eukaryotic cells   These are not specific to plants: they are found in all eukaryotic cells   resence of these components is almost enough to define a plant at the cellular level

	The tonoplast is responsible for: cell expansion, storage and digestion of water soluble molecules uptake of nutrients, sensing and cell wall synthesis storage of starch and fats
	The tonoplast is both a dumping ground and a store of water-soluble compounds. These solutes are responsible for the osmotic properties of cells, including water uptake during cell expansion.   These are functions of the plasmamembrane   Only water soluble molecules are found in the tonoplast. Starch and lipids are associated with plastids of various kinds.

	Storage of starch, green, yellow or orange pigmentation, and protein synthesis are all functions or properties of: the nucleus mitochondria plastids
	Starch and pigments are not found in the nucleus.   Starch and pigments are not found in the mitochondria.   Chloroplasts are green, chromoplasts may be orange or yellow; chloroplasts and amyloplasts may contain starch and all of these plastids are capable of protein synthesis.

	Double membrane bound organelles include: ribosomes, Golgi apparatus and tonoplast cytoskeleton, ER and plasmamembrane plastids, mitochondria and nucleus
	Ribosomes have no membrane and the other two have single membranes.   The cytoskeleton does not have a membrane, the ER is a double membrane but it does not enclose anything and the plasmamembrane is a single membrane.   Plastids, mitochondria and nucleus are all enclosed by a double membrane (two lipid bilayers) and each contains DNA

Movement of material inside the cell is a feature or function of: the endomembrane system and cytoskeleton plastids and nucleus mitochondria and ribosomes

The endomembrane system is involved in membrane traffic from ER through the Golgi to the plasmamembrane; actin and tubulin filaments are responsible for a lot of the visible movement of structures inside plant (and other cells)   Plastids themselves may move and molecules may move in or out of the nucleus, but these are not the main pathways of movement in themselves.   Mitochondria may provide the energy for movement and ribosomes may move along an RNA molecule, but htese are not the pathway of cellular movement as such.

Cell division in plants occurs: only in the embryo in meristems only at the shoot or root tip

Certainly the embryo is a mass of dividing cells, but cell division continues throughout the life of the plant.   Yes meristems include those at the apex but also the primary meristems that establish the tissue systems of the plant and lateral meristems responsible for secondary growth.   These are the apical meristems and the ultimate origin of all of the cells in the plant but division occurs elsewhere.

	The cell walls of collenchyma cells in a leaf petiole typically contain a lot of: pectin pectin and cellulose lignin
	Not just pectin (this would make them rather "squishy"   Yes, collenchyma has thickened primary walls, which means that they are basically pectin and cellulose.   Collenchyma has primary walls and these do not normally contain lignin.

	A cell can expand when the water potential in its vacuole is: lower than outside higher than outside equal to outside
	Water always moves down a water potential gradient, so it will move into the vacuole and the cell will enlarge.   In this situation water would move out of the cell. This might lead to plasmolysis in a root in saline soil or wilting of a leaf in dry air.   In this situation water cannot be taken up and so the cell cannot enlarge; it will be on the point of wilting.

	Photosynthetically active chloroplasts are present in: all epidermal cells leaf epidermal cells guard cells
	That can't be true, what about root epidermis?   Although leaves are green most of the epidermal cells do not have functional chloroplasts.   Yes, guard cells do have chloroplasts that are involved in stomatal opening.

	Water-conducting cells that lose their cytoplasm at maturity but retain their end walls are: vessel elements tracheids sieve tube elements
	Its all true except vessels lose their end walls.   Tracheids retain their end walls and are characteristic of gymnosperm wood , although they are also present in angiosperms.   Sieve tubes keep their cytoplasm at maturity; although we think of them as food transport cells, water does move with the sugars and other compounds.

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