Bio Lab

nabil choudhury biology-honors mrs. ermi 10 may 2006

plant anatomy lab laboratory objectives: after completing this lab topic, you should be able to: 1. identify and describe the structure and function of each cell type and tissue type. 2. describe the organization of tissues and cells in each plant organ. 3. relate the function of an organ to its structure. 4. describe primary and secondary growth and identify the location of each in the plant. 5. relate primary and secondary growth to the growth habit (woody or herbaceous). 6. discuss adaptation of land plants to the terrestrial environment as illustrated by the structure and function of plant anatomy. 7. apply your knowledge of plants to the kinds of produce you find in the grocery store.

answers: 18.1: plant morphology 1. q: describe proposed functions (more than one) for each organ. a: stems - stems provide support and shape of the plant. they facilitate nutrient transport and function as a central hub. in addition, the stem often provides a role in storage (starches, etc.) and photosynthesis.

roots - roots aid water and nutrient absorption and provide anchorage. in addition, roots are a storage facility for many plants. leaves - leaves function as the primary synthetic organ. in addition, leaves support transpiration through stomata and permit water flow. 2. q: imagine that you cut each organ---roots, stems, and leaves---in cross section. sketch the overall shape of that cross section in the margin of the lab manual. remember, you are not predicting the internal structure, just the overall shape. a: root: o

stem: o

leaf:

18.2: plant primary growth and development 1. q: describe the changes in cell size and structure in the stem tip. begin at the youngest cells at the apex and continue to the xylem cells. a: as the smaller cells in the stem tip progress upwards, they become bigger and longer. at the same time, their cell walls become thicker. 2. q: the meristems of plants continue to grow throughout their lifetime, an example of indeterminate growth. imagine a 200-year-old oak tree, with active meristem producing new buds, leaves, and stems each year. contrast this with the growth pattern in humans. a: humans feature determinate growth. eventually, at a certain point, growth almost stops with only necessary facilitating cell divisions taking place. consistent development is not possible within humans to a certain point. meanwhile, plants continually develop. 18.3: cell structure of primary tissues a. stems 1. q: which are larger and more distinct, xylem or phloem? a: xylem; this is in part due to the distinct size of xylem vessels and tracheids.

2. q: what types of cells provide support of the stem? where are these cells located in the stem? a: sclerenchyma are dead, fibrous, thick-walled cells that provide support to the phloem tissue. they appear in a cluster as a bundle cap. collenchyma are located, and provide support for, the epidermis. 3. q: for the cells described in your preceding answer, how does their observed structure relate to their function, which is support? a: sclerenchyma have thick walls purely purposed towards rigid support for the phloem cells. the collenchyma cells have cell walls not quite as thick, permitting strength with flexibility. they are strong and pliable so as to not snap in unfavorable conditions such as heavy winds. 4. q: what is the function of xylem? of phloem? a: xylem transports water and inorganic nutrients upwards in the plant through the roots. phloem distributes organic compounds throughout the plant in all areas and directions. 5. q: the pith and cortex are made up of parenchyma cells. describe the many functions of these cells. relate parenchyma cell functions to their observed structure. a: parenchyma serve the primary purpose of storage, and secondarily as photosynthetic and support cells. essentially, they are large, commodious organelles (vacuoles) for storage. when filled with water, their turgor pressure is at maximum and they press on the cell wall; a state known as being turgid. 6. q: what differences did you observe in the prepared stem sections and your hand sections? what factors might be responsible for these differences? a: the differences in colors and quality lend themselves to the use of staining, agents, and professional processing.

b. roots which of the four functions of roots listed in the introduction to this lab do you think is related to these cortical cells and their organelles? starch storage. 1. q: suggest the advantage of taproot and fibrous roots under different environmental conditions. a: taproots are suitable for many types of earthy soils, as they penetrate deep into the soil for anchorage and to absorb nutrients. fibrous roots are suitable for loose, wet soil and aqueous environments as their large surface area and dispersed, fibrous roots better absorb nutrients while sacrificing anchorage. 2. q: did your observations support your hypothesis and predictions? a: not applicable. 3. q: compare the structure and organization of roots and stems. how do these two organs differ? a: roots possess an internal endodermis to guard the vascular tissue, as well as the casparian strip as an adjacent cell guard. this structure allows for water retention within the root and inhibits water loss back into the soil. root hairs on the root increase surface area for nutrient and mineral absorption. roots have designated vascular tissue in the center, with no piths. stems possess chlorophyll more often than roots, and possess a ring of vascular tissue systems around a central pith. shoots and buds are exclusive to the stem as well. 4. q: explain the relationship of structure and function for two structures or cells found only in roots. a: root hairs are long and threadlike secondary projections of roots that increase the surface area of the root for augmented absorption. the waxy endodermis regulates what enters and exits the central vascular tissues, permitting

greater retention of water and preventing water from returning to the soil. the cortex is the storage location for roots. 5. q: note that the epidermis of the roots lacks a cuticle. can you explain why this might be advantageous? a: the absence of a waxy cuticle permits a more complete absorption of water and minerals into the root. 6. q: what is the function of the endodermis? why is the endodermis important to the success of plants in the land environment? a: the endodermis regulates the materials that enter and exit from the vascular tissue. the endodermis allows for land plants to retain and release desired and undesired matter more effectively. it is primarily used to aid in water retention, forcing water into the vascular tissue and preventing water from returning to the soil. c. leaves is xylem or phloem on top in the leaf? xylem. observe the distribution of stomata in the upper and lower epidermis. where are they more abundant? stomata are more abundant in the lower epidermis. 1. q: describe the functions of leaves. a: leaves are organs especially adapted for photosynthesis. the thin blades provide large comparative surface area for the absorption of light and uptake of carbon dioxide through stomata. 2. q: provide evidence from your observations of leaf structure to support the hypothesis that

structure and function are related. be specific in your examples. a: the leaves possess a large surface area for increased absorption of light. in addition, the stomata and guard cells aid water retention and facilitate carbon dioxide uptake and oxygen release. the mesophyll provides area for necessary gas exchange and water storage. 3. q: explain the observation that more stomata are found on the lower surface of the leaf than on the upper. a: there are more stomata found on the lower surface of the leaf less water is traditionally lost through lower stomata. carbon dioxide and oxygen are exchanged in this area, making water loss more difficult and simultaneously more controlled. 4. q: explain the differences observed, if any, between the stomata from leaves kept in light and dark environments. a: in light, the stomata were open because photosynthesis was occurring. they were turgid because the influx of k+ ions allowed water to diffuse into the cell and cause the pore to open. in the dark environment, the stomatal guard cells were limp and flaccid as photosynthesis could not occur. 18.4: cell structures of tissues produced by secondary growth 1. q: what has happened to the several years of phloem tissue production? a: the phloem after several years forms into a barky material through aging, cell death, and layering. 2. q: based on your observations of the woody stem, does xylem or phloem provide structural support for trees? the xylem, or "wood," essentially provides the bulk of structural support for trees. 3. q: what function might the ray parenchyma cells serve?

a: the ray parenchyma cells may very well serve to facilitate transport of materials laterally along the woody stem. 4. q: how might the structure of early wood and late wood be related to seasonal conditions and the function of the cells? think about environmental conditions during the growing season. a: the early wood is formed when growth is comparatively rapid, hence its given structure within the woody stem to develop the woody xylem inwards. the late wood is often later into the season, when growth is not quite as rapid and it is preferable to layer outwards. 18.5: grocery store botany: modifications of plant organs 1. q: what feature of the white potato provided key evidence in deciding the correct plant organ? a: the leaf buds, or “eyes” distinctly indicate that the white potato is, in fact, a stem. 2. q: based on your knowledge of the root, why do you think roots have been selected so often as food sources? a: since roots are often used to stockpile reserves, they are packed with starch and carbohydrates for relatively large amounts of filling energy and calories. 3. q: what characteristics of sieve-tube structure provides a clue to the role of companion cells? a: the small pores at the sieve plates with the plasmodesmatal structures lend themselves to the presence of companion cells. companion cells are integral as a "cellular lifeline," performing basic cellular functions for the sieve tubes. 4. q: compare primary and secondary growth. what cells divide to form primary tissue? to form secondary tissue? can a plant have both primary growth and secondary growth? explain, providing evidence to support your answer. a: primary growth is primarily involved with the lateral growth of plants. this growth often occurs at primary meristems. cambium cells provide secondary growth, or girth. it is possible to

undergo both primary and secondary growth modes simultaneously. trees are ideal examples of this as they actively grow taller and thicker. applying your knowledge 1. q: cells of the epidermis frequently retain a capability for cell division. why is this important? (hint: what is their function?) a: the epidermis serves to protect the plant and to regulate the movement of materials. as a plant grows or undergoes any type of damage, the ability of the epidermis to divide allows the plant to heal and cover exposed tissues. 2. q: why is the endodermis essential in the root but not in the stem? a: the endodermis forces water in the root into the xylem while preventing it from returning to the soil. it is essential for water retention. 3. q: when lateral roots grow outward from the pericycle, what effect does this have on the cortex and epidermis? (hint: review the structure of the root and the location of these tissues.) a: as lateral roots grow outward from the pericycle, the cortex and epidermis are forced to expand in order to accommodate increased surface area. 4. q: the belt buckle of a 20-year old man may be a foot higher than it was when he was 10, but a nail driven into a 10-year-old tree will be at the same height 10 years later. explain. a: primary tree growth occurs at the top of the shoot, in the apical meristem. human growth occurs throughout the body. 5. q: explain from a cellular point of view how it is possible to determine the age of a tree. a: it is possible to determine the pattern of growth within the xylem and phloem to assign an overall age to a tree. ray parenchyma cells provide clues as well as the xylem “rings.” 6. q: the oldest living organisms on earth are plants. some bristlecone pines are over 4,000 years

old, and a desert creosote bush is known to be 10,000 years old. what special feature of plants provides for this incredible longevity? how do plants differ from animals in their pattern of growth and development? a: plants feature alternation of generations which ensures propagation according to the suitability of the respective environmental conditions. 7. q: plant cells have cell walls and animal cells do not. how does this difference relate to differences in plant and animal function? a: in plants, water retention is much more important than in animals. the cell wall helps to prevent water loss. in addition, since most plants are relatively immobile, cell walls bolster plant protection to environmental and ecological factors and conditions. 8. q: many of the structural features studied in this laboratory evolved in response to environmental challenges of the terrestrial habitat. complete table 18.3.

charts and tables table 18.1: grocery store botany name of item

plant organ

function/features

potato

stem

storage

sweet potato

root

storage

tomato

fruit

reproduction

grapes

fruit

reproduction

oranges

fruit

reproduction

celery

stem

support

cabbage

leaf

photosynthesis

lettuce

leaf

photosynthesis

apple

fruit

reproduction

banana

fruit

reproduction

table 18.2: structure and function of plant cells cell type

structure

function

plant organ

epidermis

flattened, rectangular

protection, regulates movement of materials

stems, roots, leaves/dermal

parenchyma

thin walled, large vacuoles

photosynthesis, support, storage of materials, lateral transport

stems, roots, leaves/ground

collenchyma

large vacuoles, uneven thickening of cell walls

flexible support

stems, roots, leaves/ground

sclerenchyma

thickened walls with lignin

strength and support, dead at maturity

stems/ground

tracheids

long, thin cells with perforates, tapering ends

water-conducting cells

stems, roots/vascular

vessels

open-ended cells joined end-to-end

water-conducting cells, transport materials

stems, roots/vascular

sieve tubes

open-ended cells joined end-to-end, no nucleus

phloem, organic conducting cells

stems, roots, leaves/vascular

endodermis

thick cells surrounded by waxy casparian strip

water retention in root, guides water to xylem

roots/dermal

primary meristems

small, actively dividing cells

produce primary lateral plant tissues throughout plant life

stems, roots (shoots, tips)/unspecialized

cambium

small, actively dividing cells

produce secondary plant tissues throughout plant life

stems/vascular (unspecialized)

guard cells

sides of stomata, cells capable of swelling to close

regulate water use and carbon dioxide uptake

leaves/dermal

periderm

thick walls impregnated with waxy suberin

replaces function of epidermis and cortex, derived from cork cambium, dead at maturity

stems/dermal

ray parenchyma

ringlike “ray” structured cells circularly radiating from center

lateral transport of materials

stems/vascular

table 18.3: adaptations of plant cells and structures to the land environment environmental factor

adaptations to land environment

desiccation

endodermis, stomata, cuticle (prevent water loss)

transport of materials between plant and environment

vascular tissues, endodermis, stomata

gas exchange

stomata

anchorage in substrate

roots (taproot, fibrous), root hairs

transport of materials within plant body

vascular tissues (phloem, xylem)

structural support in response to gravity

dermal tissues, collenchyma

sexual reproduction without water

seeds

dispersal of offspring from immobile parent

seed adaptations (wings), flowers (pollination)