Exam 2 Flashcards
Briefly describe the history of the discovery of cells.
Cells were discovered by Robert Hooke in the 1660s when he looked at cork cells (outer tree bark) through a microscope- called them “cells” bc reminded him of monk’s rooms in the monastery.
How does the structure of a prokaryotic cell differ from that of a eukaryotic cell?
-Prokaryotes have no nucleus, the DNA is unbound in a region known as the nucleoid.
They do not have membrane bound organelles and cytoplasm bound by plasma
membrane.
-Eukaryotic cells have DNA in double-membraned nucleus, have membrane bound
organelles, much larger than prokaryotes
What are the differences between plant and animal cells?
Plants:
-Cell walls
-Cell plate and plasmodesmata
-Plastids and vacuoles
Animals:
-Internal or external skeletons; no cell walls
-Plasma membrane is called a cell membrane.
-Divide by pinching in two; no cell plate nor plasmodesmata
-Centrioles present during cell division.
-No plastids nor vacuoles
Describe the various plant cell organelles and their roles.
Cell Wall
- Mainly composed of cellulose (long glucose chains)
- Matrix of hemicellulose (holds cellulose together), pectin (gives stiffness), and glycoproteins
Plasmodesmata (cell communication)
- Cytoplasmic strands that extend between cells thru small openings, allow for movement of
fluids and dissolved substances
Plasma membrane
- Phospholipid bilayer w/ proteins dispersed throughout- selectively permeable for movement
of subs in/out of cell
Nucleus
- Control center, contains DNA
- Nuclear envelope consists of two membranes
- Pores on surface of envelope, also selectively permeable
Endoplasmic Reticulum
- Flattened sacs and tubes forming channels throughout cytoplasm
- Cell communication, organelle membrane synthesis, protein modification
- Rough ER: ribosomes on outer surface, for protein synthesis/storage
- Smooth ER: lipid secretion
Dictyosomes
- Stacks of flattened discs or vacuoles
- Building blocks of golgi bodies in animals, but don’t pack tightly enough in plants to form
same structure
- Modify carbohydrates, assemblage and collection of polysaccharides
Plastids
- Chloroplasts are the main ones
- Contain grana made of thylakoids
- Thylakoid membranes contain chlorophyll, first steps of PS occur here
- Stroma: matrix of enzymes involved in PS- circular DNA molecule that encodes
production of PS proteins
- Other plastids include chromoplasts (carotenoids) and leucoplasts (starches and oils)
Mitochondria
- Release E from cell resp
- 2 membranes
- Inward membrane forms numerous folds (cristae ) to increase surface area in matrix
which includes DNA and RNA
Vacuoles
- Up to 90% volume in mature cells
- Tonoplasts- vacuolar membranes
- Filled with watery fluid called cell sap containing salts, sugars, proteins, acids, and
anthocyanins
- Help maintain cell pressure and pH, storage of cell metabolites and waste products
Cytoskeleton
- Network of microtubules and microfilaments
- Microtubules control addition of cellulose to cell wall, move flagella and cilia
- Microfilaments: cytoplasmic streaming
Describe plant tissues.
Three or four major groups of organs:
-Roots
-Stems
-Leaves
-Flowers
Each organ is composed of tissues
-A tissue is a group of cells performing a similar function
-There may be more than one tissue per organ
List and describe plant meristems and where they are found.
Meristems are permanent regions of cell growth and differentiation- cells contain very large nuclei and have small/absent vacuoles.
Apical meristems are found at the tips of roots and shoots, allowing them to increase in length
Primary meristems → primary tissues
- Protoderm → epidermis
- Ground meristems → pith (stems), cortex (roots), mesophyll (leaves)
- Procambium → primary xylem and phloem
Secondary meristems → secondary tissues (increase width of roots and stems)
- Not found in all plants
- Cork cambium → periderm
- Lies outside vascular cambium just inside outer bark- produces cork (bark)
- Vascular cambium → secondary xylem and phloem (support and conduction)
Intercalary meristems- found in grasses and plants w no secondary meristems. Located around
nodes along stems, add to stem length
State the difference between simple and complex tissues.
Simple tissues have one type of cell, while complex tissues have many types of cells
Identify examples of simple and complex tissues.
Simple tissues- parenchyma, collenchyma, sclerenchyma
Complex tissues: epidermis, periderm, xylem, phloem
Describe three types of simple tissues and where they may be found in the plant.
Parenchyma
collenchyma
sclerenchyma
parenchyma
- Thin, pliable walls (up to 14)
- Cytoplasm has various vacuoles and secretions
- Remain alive for a long period
- Space in between cells
- Found in almost all parts of higher plants
- Edible part of fruits and vegetables
- PS, storage, transfer between cells
- Aerenchyma- parenchyma tissue with extensive connected air spaces (aquatic plants)
- Chlorenchyma- have chloroplasts
- Transfer cells- irregular extensions of cell wall that increase SA of plasma membrane
collenchyma
- Thick cell walls (uneven thickness)
- Pliable and strong, provide flexible support
- Located just below epidermis in leaves, stems, flowers
- Celery string
Sclerenchyma
- Thick, tough secondary walls saturated with lignin
- Dead at functional maturity, function in support
- Sclereids: stone cells scattered in tissue (nuts, seed coats, peach pits, etc)
- Cells as long as they are wide
- Protection, support, prevent drying out
- Fibers: roots, stems, leaves, fruits
- Much longer than wide, provide support
- Have tiny cavities (lumen)
- Used for string, textile, canvas, etc
Explain the structural and functional differences between xylem and phloem.
XYLEM
- Transport water, ions, water-soluble nutrients from roots throughout plant
- Composed of parenchyma cells, fibers, vessels, tracheids, ray cells
- Vessels- long tubes with perforated plate at end
- Tracheids- tapered at end with pairs of pits allowing water to pass from cell to cell,
dead at maturity
- Rays- long lived parenchyma cells function in lateral conduction and food storage
PHLOEM
- Conduct dissolved PS materials throughout plant
- Composed of sieve tube members, companion cells, fibers, parenchyma cells, ray cells
- Sieve tube members: no secondary cell wall or nuclei, lay end to end. Plates with
small pores to allow passage thru sieve tube. Plugged when a cell is injured
- Companion cells: narrow, tapered cells associated w. Sieve tube members
Describe the structure and function of the epidermis, periderm, and secretory tissues.
Epidermis
- The epidermis is a one-cell thick protective layer around all plant organs that consists of
parenchyma cells and some specialized cells
- Cutin: fatty substance on outside of cell wall that forms cuticle, which secretes wax
- Prevents evaporation, resistance to pathogens
- Root epidermal cells → root hairs to increase root surface absorption area
- Leaves have stomata bordered by guard cells
- Some epidermal cells have hairs or secrete
- Secretory cells: flower nectar, citrus oils, latex, resins
Periderm
- Comprises outer bark of woody plants
- Consists mainly of cork cells and some parenchyma cells
- Replaces epidermis when cork cambium begins producing tissue
- Cork cells dead at maturity- suberin injected into cells that waterproofs them
Secretory tissue
-Secretory cells may function individually or as part of a secretory tissue
ex. Flower nectar, Citrus oils, Glandular hair, mucilage, Latex, resins
Describe human uses of different plant tissues.
- Use sclerenchyma fibers for rope, textiles, string, canvas
- Use wood for construction
