Plants - Chapter 12

Question 1

Plants

Answer 1

plants are the foundation on which most terrestrial ecosystems are built
are the primary producers in most systems, through the process of photosynthesis
plants serve as the first link in the food chain which affects all species of animals in the system

Question 2

Xylem

Answer 2

xylem consists of two cell types, both with secondary walls and both dead at functional maturity
tracheids = long, thin tapered cells with pits (thinner regions with primary cell walls only), water flows from cell to cell through pits, they also function as support
vessel elements = wider, shorter, thinner-walled and less tapered than tracheids, aligned end-to-end, end walls are perforated permitting flow of water through long chains of vessel elements called xylem vessels

Question 3

Phloem

Answer 3

sieve tube members are chains of phloem cells that transport sucrose, other organic compounds, and some minerals
the cells are alive at functional maturity
the end walls have pores and are called sieve plates
the pores probably facilitate the movement of fluid between cells
at least one companion cell is connected to each sieve tube member and services the sieve tube member because this cell lacks a nucleus and ribosomes

Question 4

Sieve tubes

Answer 4

sieve tubes carry food from a sugar source to a sugar sink, so the direction in a given tube is variable
a sugar source is a plant organ where sugar is being produced (leaves)
a sugar sink is an organ that consumes or stores sugar (roots/shoots/fruits)

Question 5

Meristem

Answer 5

unspecialized cells
divide to generate new cells near the growing points of the plant (root and shoot tips)
apical meristems = located in root tips and shoot buds, supply cells for plant to grow in length
lateral meristem = cylinders of dividing cells extending along the lengths of roots and shoots, provides secondary dermal tissues which are thicker and tougher than original epidermis, adds new layers of vascular tissues

Question 6

Types of growths

Answer 6

primary growth = for elongation

secondary growth = for increased girth, thickening of roots and shoots which occurs in woody plants

Question 7

Root hairs

Answer 7

absorption of water is greatly enhanced by root hairs, which increase the surface area of the root
root hairs are normally most numerous near the root tips
water and mineral absorption are also enhanced by mycorrhizal fungi, symbiotic associations between roots and fungi

Question 8

Typical root structure

Answer 8

root cap = protection for the growing tip of the root, protects meristem tissue
zone of division = active mitosis happens here, apical meristem located here
zone of elongation = prior to cell walls solidifying completely, cells are stretching to their final length, pushing the root through the soil
zone of differentiation/maturation = cells begin to specialize in structure and in function

Question 9

Gas exchange in roots

Answer 9

one function of roots is to achieve gas exchange with soil
oxygen will diffuse in if all the requirements are met
requirements = surfaces are moist, oxygen is present in surrounding area, carbon dioxide is present within the cells, all inner cells have contact with the surrounding environment

Question 10

The shoot system

Answer 10

shoot systems are comprised of vegetative shoots and floral shoots
vegetative shoots consist of a stem and attached leaves, may be the main shoot or a vegetative branch
floral shoots terminate in flowers

Question 11

Role of stems

Answer 11

connect the vascular tissue in the roots to that of the leaves
raise and support leaves to maximum exposure to sunlight
support flowers and maximize opportunity for pollination
in some plants, storage of water and/or carbohydrates

Question 12

Herbaceous stems

Answer 12

stems that never harden into wood
monocot stem = vascular bundles scattered throughout the stem
dicot = vascular bundles arranged around outer edge of the stem, xylem to the inside, phloem to the outside

Question 13

Woody stems

Answer 13

most woody angiosperms are dicots
vascular cambium = layer of cells in the vascular tissue that divide to form new xylem and phloem cells, critical for any plant stem forming woody material

Question 14

Wood

Answer 14

many layers of xylem cells
sapwood transports water and minerals while heartwood does not
annual rings = xylem from one growing season
cork cambium = layer of cells that produces cork, the tough outer layer of the tree trunk/stem
cork prevents water loss and protects from infection and parasites

Question 15

Gas exchange in stems

Answer 15

young green stems photosynthesize

woody stems have lenticels to permit gas exchange by living cell layer within trunk

Question 16

Leaves

Answer 16

primary site of chloroplasts = organelles in which photosynthesis takes place
carbon dioxide and water and sun’s energy produces oxygen and glucose
allows for gas exchange between interior of plant and external environment

Question 17

Leaf structure

Answer 17

simple leaves and compound leaves
cloaked by upper and lower epidermis of tightly interlocking cells, which protects against physical damage and pathogens
waxy cuticle prevents water loss
stomata pores flanked by guard cells that regulate gas exchange and allow transpiration (typically on underside)

Question 18

Palisade mesophyll

Answer 18

directly under epidermis
tightly packed columnar cells
one or two layers packed lengthwise
rich in chloroplasts

Question 19

Spongy mesophyll

Answer 19

between palisade mesophyll and lower epidermis
irregularly shaped
randomly arranged with air spaces between them for gas exchange
lower concentration of chloroplasts

Question 20

Adaptations

Answer 20

many variations in leaves provide for better survival in specific habitats
thickened epidermis and epidermal hairs protect and minimize water loss for leaves of dry areas
large air spaces make floating leaves buoyant

Question 21

Into the root

Answer 21

water concentrations in roots cells is lower than in soil, so diffusion is sufficient, and moves either from cell to cell or travels between cells
nutrient concentrations are higher in cells than in soil, so active transport is necessary, and all nutrients travel from cell to cell
when water and nutrients meet the endodermis, they hit the Casparian strip, a waxy barrier between ground tissue and vascular cylinder
all substances are forced one way through cells and active transport occurs

Question 22

Transport of water

Answer 22

xylem sap moves against gravity due to root pressure
active transport of ions or water into roots is likely
relies on the adhesive properties of water
in small tubes, water is attracted by the polarity of capillary walls
water is pulled up the plant
as one water molecule evaporates from leaf (transpiration), another molecule takes its place

Question 23

Transport of sugar

Answer 23

loading of sugar into sieve tubes (phloem) at source reduces water potential inside, causing tubes to take up water from surrounding tissues by osmosis
this absorption of water generates a hydrostatic pressure that forces the sap to flow along the tube
pressure in the tube is reinforced by the unloading of sugar and the consequent loss at the sink
sugar does not accumulate in sink cells because it is either consumed or converted into storage compounds

Question 24

Mass-flow theory

Answer 24

sugar is highly concentrated in one area of a plant (leaves)
water moves in to dilute and create equilibrium
creates pressure that forces flow into available space (other phloem vessels)

Question 25

Problems with mass-flow theory

Answer 25

pressure doesn’t seem to build up in phloem
doesn’t account for speed of transport
doesn’t explain simultaneous bi-directional flow