BISC 208: Mini-Exam 1

Plants display indeterminate growth

- "unrestricted" growth • final body size/shape is determined strongly by the environment ↳ resources ↳ predators ↳ where/how much light • unlike animals (controlled stopping point) - modular • *module* = stem + axillary bud + leaf • plant = repeated modules

TH: Stages in the origin of life

- (1) abiotic synthesis of organic molecules - (2) polymerization → monomers assembled into polymers - (3) package into lipid bilayer → creates different internal chemical environment - (4) self-replication of molecules

RG: Define adhesion

- *adhesion*: the tendency of certain dissimilar molecules to cling together due to attractive forces

RG: Define apical meristems. Where are they located?

- *apical meristem*: a group of undifferentiated plant cells, at the tip of a shoot or root, that is responsible for primary growth

RG: Define capillary action

- *capillary action*: the tendency of water to move up a narrow tube due to adhesion, cohesion, and surface tension

RG: Define cohesion

- *cohesion*: the tendency of certain like molecules (e.g. H2O) to cling together due to attractive forces

RG: What is the cohesion-tension theory? Sketch the process

- *cohesion-tension theory*: the theory that water movement upward through plant vascular tissues is due to loss of water from leaves (transpiration), which pulls a cohesive column of water upward

RG: What is a cuticle, where is it located, and what is its function?

- *cuticle*: a protective coating secreted by the outermost layer of cells of an animal or a plant; often functions to reduce evaporative water loss - located on stems and leaves

RG: Define the dermal tissue (aka epidermis) of plants. What is its primary function? Where is it located?

- *dermal tissue/ epidermis*: the tissue forming the outer layer of a plant/ outermost layer of cells of any multicellular organism - function is to protect the plant from water loss, diseases, and herbivores - found in both roots and shoots

RG: Define the ground tissue system. What are the functions of ground tissue? Where are these tissues located?

- *ground tissue system*: most common of the tissue systems; includes the following tissues/cell types → parenchyma, collenchyma, and sclerenchyma — tissues other than the epidermis and vascular - responsible for synthesis and storage [pigments, hormones, toxins for defense] - found in cells and the stem

RG: Define osmosis

- *osmosis*: diffusion of water across a selectively permeable membrane from a region of lower [solute] (higher [water]) to a region of higher [solute] (lower [water]). for osmosis to occur, the solute would not be able to pass through the membrane

RG: Define the term *phenotypic plasticity*. What does this mean in the context of root system, and why is it important for plant survival?

- *phenotypic plasticity*: variation in phenotype that is due to difference in environmental conditions. occurs more commonly in plants than animals - changeable root systems based on the environment (ability to adapt)

RG: What is the function of the phloem?

- *phloem*: plant vascular tissue that conducts sugar between roots and shoots; contains sieve-tube elements and companion cells. primary phloem develops from the procambium of apical meristems; secondary phloem develops from the vascular cambium

RG: Define pressure potential

- *pressure potential*: a component of the potential energy of water caused by physical pressures on a solution - can be positive or negative

RG: What types of tissues can primary meristems differentiate in to?

- *primary meristems*: in plants, three types of partially differentiated cells that are produced by apical meristems → protoderm, ground meristem, and procambium

RG: What is secondary growth? What is its major function?

- *secondary growth*: in plants, an increase in the width of the stems and roots due to the activity of the cambium - function → to increase the amount of conducting tissue available and provide the structural support required for extensive growth

RG: Name the two systems plants use to acquire resources

- *shoot system*: above ground part of a plant that is made up of stems, leaves, and flowers - *root system*: below ground part of a plant

RG: What are some examples of diversity in leaves?

- *simple leaf*: single blade defined by the presence of a single axillary bud where the petiole joins the branch or stem - *blade*: a wide, flat part of a plant leaf - *compound*: consisting of 2 or more blades but defined by the presence of a single axillary bud where the petiole joins the branch or stem

RG: Define solute potential. How does it impact movement of water?

- *solute potential*: a component of potential energy of water caused by a difference in solute concentrations at 2 locations. can be zero (pure water) or negative - they are measured related to the solute potential of pure water - solutions with [high] of solutes have low solute potential

RG: Define each of the following aspects of the shoot system: - Stems - Nodes - Leaf - Axillary Bud - Branch - Apical Bud

- *stem*: vertical, aboveground structures that make up the shoot system of plants - *nodes*: the part of a stem where leaves or leaf buds are attached - *leaf*: the most photosynthetic organ of vascular plants - *axillary bud*: a bud that forms at a node and may develop into a lateral (side) branch - *branch*: a lateral extension of a plant's shoot system - *apical bud*: a bud at the tip of a stem or branch, where growth occurs to lengthen the stem or branch

RG: What is the function of stomata? What is the role of guard cells in stomata function?

- *stomata*: a microscopic pore on the surface of a leaf or stem through which gas exchange occurs; typically surrounded by specialized cells that open the pores - *guard cells*: one of two specialized, crescent-shaped cells forming the border of a plant stroma. can change shape to open or close the stomata

RG: Define surface tension

- *surface tensions*: the cohesive force that causes molecules at the surface of a liquid to stick together, thereby resisting deformation of the liquid's surface and minimizing its surface area

RG: Define tracheids and vessel element. What are the similarities and differences?

- *tracheids*: a long, thin, water-conducting cell that has pits where its lignin-containing secondary cell wall is absent, allowing water movement between adjacent cells - *vessel element*: a short, wide, water-conducting cell that has gaps through the primary and secondary cell walls, allowing unimpeded passage of water between adjacent cells - similarities • water-conducting • both allow movement between adjacent cells - differences • tracheids are long and thin while vessels are short and wide

RG: Define transpiration. What is the primary unit of measurement for transpiration?

- *transpiration*: loss of water vapor from above ground plant parts. occurs primarily through stomata - measured in mg/m^2

RG: Define the vascular tissue system

- *vascular tissue system*: tissues that transports water, nutrients, and sugars. made up of the complex tissues xylem and phloem, each of which contains several cell types

RG: What is the function of xylem tissue? Which of the three tissue systems does this belong to?

- *xylem tissue*: vascular tissue that conducts water and ions from the roots to shoots; contains tracheids and/or vessel elements - primary xylem develops from the procambium of apical meristems; secondary xylem, or wood, from the vascular cambium

Tissue Systems

- 3 tissue systems • *dermal* → protection ↳ ex: waxy cuticle on the leaf, bark on a tree trunk, thorns • *ground* → storage, support, photosynthesis ↳ store sugars and water ↳ support to hold plants upright ↳ photosynthesis • *vascular* → transportation ↳ transports sugars and water - tissue systems are continuous in plants • vary in appearance in different organs

MB: Ground tissue is indicated by the letter __________

- A

MB: Xylem is indicated by the letter __________

- D

MB: The region surrounded by guard cells is indicated by the letter __________

- D • guard cells regulate the opening and closing of stomata

MB: Pith is indicated by the letter __________

- E

TH: Where do you think this plant lives? (wk 2 → leaves)

- a desert (not the same picture as on tophat)

MB: In which of the following condition would transpiration be expect to be highest?

- a hot, dry, and windy day • would tend to result in transpiration to be highest, particularly if the plant is not under water stress

MB: Which of the following cell types retains the ability to undergo cell division?

- a parenchyma cell near the root tip

RG: Why is a large surface area/volume ratio important for a plant to be efficient?

- a plant body is more efficient as an absorption-and-synthesis machine when it is able to capture more light

What is a land plant?

- a plant that is a multicellular eukaryote that is often photosynthetic - plants differ from all other organisms by having ... • an *apical meristem*: how plants can grow indeterminately and don't reach a stopping point • a lifecycle that exhibits alternation of multicellular generations (haploid/diploid versions) • thick-walled spores (1N) that can grow into haploid plants (gametophytes) • multicellular sex organs

Review: Water and Life

- basics of water movement same for all • water is NOT actively pumped between cells - water moves *passively* by *osmosis*: diffusion of water across a semi-permeable membrane • *diffusion*: the tendency of a substance to move down its concentration gradient • *semi-permeable membrane*: water moves passively, often solutes do not ↳ large and charged particles need channels and carriers to move through membranes - osmosis describes the diffusion of water across a semipermeable membrane

MB: The value for Ψ in root tissue was found to be -0.15 MPa. If you take the root tissue and place it in a 0.1 M solution of sucrose (Ψ = -0.23 MPa), the net water flow would __________

- be from the tissue into the sucrose solution

RG: What is the role of tracheids and vessel elements in water transport?

- both help in the conduction of water along the stem and provides mechanical support to the plant

TH: Where does the mass of a tree come from?

- carbon dioxide

Cohesion-Tension Model

- cohesion • water column in the xylem • hydrogen bonds between H2O molecules - tension (- Ψp) • from evaporating water in leaves • pulls column upward - adhesion • h-bonds with xylem walls • helps counter gravity - water moves up by moving down its Ψ gradient

Challenges of Moving to Land

- communication between cells • *plasmodesmata*: pores between cells ↳ they need these because they have a cell wall that prevents molecules from easily diffusing - *desiccation*: to dry out • many adaptations - gas exchange • *stoma*: pores on leaves and stems ↳ allow for the entry of CO2 ↳ open and close at certain times (not always open) - sexual reproduction • alternation of multicellular generations (organisms have both haploid and diploid multicellular stages) • gametes cannot swim to each other anymore, at risk of desiccation

MB: The veins of leaves are __________

- composed of xylem and phloem - continuous with vascular bundles in the stem and roots - finely branched to be in close contact with photosynthesizing cells

MB: The surface area of a plant's root system is substantially larger than the surface area of its shoot system. The extensive surface area of roots is an adaptation associated with __________

- contact with soil particles for mineral and water absorption

MB: The letter A indicates the __________ (different diagram, question 9)

- cortex

RG: The pressure exerted by water vapor in the atmosphere is dependent on what two factors?

- depends on temperature and humidity

RG: Define a perennial root system

- describing a plant whose life cycle normally lasts for more than one year

MB: The letter A indicates the __________

- epidermis • the epidermis is the outmost layer of tissue

Putting Water Potential Together

- equation: Ψ = Ψp + Ψs

MB: The water lost during transpiration is a side effect of the plant's exchange of gases. However, the plant derives benefits from this water loss in the form of __________

- evaporative cooling and mineral transport

Q2: Which of the following occurs when the plant needs CO2 for photosynthesis?

- guard cells open by pumping solutes into their cytoplasm, causing H2O to diffuse into the cell via osmosis

RG: Water moves from areas of __________ water potential to areas of __________ water potential

- high; low

TH: Why do plants transpire more water in dry environments compared to humid environments?

- humid environments have moisture in the air which allows less water from the plant to have to be transpired

TH: What type of bonds are responsible for water molecules "sticking" to each other and nearby surfaces?

- hydrogen bonds

TH: Where do you think this plant lives? (wk 2 → stems)

- in a pond (not the same picture as on tophat)

Q2: The shoots organ system includes ...

- leaves - stems - reproductive parts

MB: Most of the water taken up by a plant is __________

- lost during transpiration

Q2: Most of the water taken up by a plant is __________

- lost during transpiration

MB: Water potential is generally most negative in which of the following parts of a plant?

- mesophyll cells of the leaf

Q2: Water potential is generally most negative in which of the following parts of a plant?

- mesophyll cells of the leaf

Water, H2O

- molecules (+) on one end and (-) on the other • form hydrogen bonds [relatively weak bonds] - *cohesive*: the same type of molecules stick together • ex: surface tension - *adhesive*: molecules stick to hydrophilic surfaces (other things) • ex: inner walls of tracheids and vessels • allows water to move up the plant stem

TH: Which of the following is/are true regarding water and plant physiology?

- most water is returned to the air via transpiration as a consequence of CO2 uptake

RG: How does net movement of water occur?

- occurs as a direct result of differences in water potential from one region to another

Basic Anatomy of Plants

- organ systems (roots and shoots) - tissue systems - tissues - individual cells

MB: A student examining leaf cross sections under a microscope finds many loosely packed cells with relatively thin cell walls. The cells have numerous chloroplasts. What type of cells are they?

- parenchyma

TH: How do you think this tree moves water all the way to the leaves at the very top?

- passive transport

Pressure Potential (Ψp)

- physical pressure of water • turgor pressure of the fluid on the cell wall • wall pressure of the wall pushing back on the fluid - when pressure is negative it is called *tension* • ex: tension draws water up through the straw - moving water via pressure potential is also called *bulk flow* - water moves towards areas of lower pressure

How do plants grow?

- plant growth is indeterminate • cell division is localized to special regions called *meristems* • *meristems*: non-permanent tissues that can grow • 3 locations of meristems ↳ *apical*: plant growing in length (longer) ↳ *lateral*: plant growing in width (wider) ↳ *intercalary*: where the leaf meets the stem - developmental "fate" determined right after mitosis • which tissue they will become (dermal, vascular, or ground) • as a new module grows, some cells will turn into each type of tissues, because every part of the plant needs each type of tissue

What is an organ?

- plant organs • roots → underground • shoots → including leaves, stems, and reproductive parts

Plant Structure Wrap Up

- plants have adaptations that allow them to survive on land - plants are composed of 2 organs → shoots and roots - there are 3 tissue systems in plants • dermal • ground • vascular - plants have indeterminate growth and grow in modules • plants generate new growth from meristems

Water Potential in the Air

- pressure exerted by water vapor in the atmosphere depends on temperature and humidity - the lower the pressure potential, the faster liquid water evaporates out of the leaf into the atmosphere • water that exits as water vapor has no solute potential - dry air → fewer H2O molecules → less pressure exerted → increased evaporation - warm air → molecules further apart → lower pressure

RG: What features are found in plant cells, but not animal cells?

- primary (outer) and secondary (inner) cell walls - *plasmodesmata*: physical connections between 2 cells - chloroplasts - large vacuole - distinct tissues

Q2: Plants contain meristems whose major function is to __________

- produce more cells

MB: Which of the following cells primarily transport sugars over long distances?

- sieve-tube elements

Water Potential of Soil

- soil has few solutes and is under little pressure, therefore has higher pressure than water in the roots - since water wants to favor movement to lower pressure, this favors movement into the roots - if water pressure drops in the soil (e.g. a drought) this makes obtaining water difficult for the plant - species in dry soils adapts by lowering the solute potential of their tissues

MB: Carbon dioxide enters the inner spaces of the leaf through the __________

- stoma

MB: Photosynthesis ceases when leaves wilt, mainly because __________

- stomata close, preventing carbon dioxide from entering the leaf

MB: What is meant by phenotypic plasticity in roots and shoots?

- the ability to modify form depending on environmental conditions • remember that phenotype refers to morphological appearance, while plasticity refers to variation in phenotype in varying environments

RG: What cell organelle resists expansion of the cell?

- the cell wall resists expansion of the cell

MB: What drives the flow of water through the xylem?

- the evaporation of water from the leaves

Q2: What drives the flow of water through the xylem?

- the evaporation of water from the leaves

RG: How does vascular tissue withstand negative pressure without collapsing?

- the evolution of lignified secondary cell walls

Q2: Water molecules stick together in the process known as cohesion because:

- the partially positive hydrogen is attracted to the partially negative oxygen on another water molecule

MB: When an animal cell is placed in a hypotonic solution and water enters the cell via osmosis, the volume of the cell increases until it bursts. This does not happen to plant cells, because __________

- they have cell walls, which provide pressure to counteract the pressure of the incoming water

RG: What is the function of the root system?

- to absorb water and nutrients

Q2: Which of the following would tend to most directly increase transpiration?

- too much sunlight

MB: Which structure is correctly paired with its tissue system?

- tracheid → vascular tissue

MB: Water transport is the primary function of which cell type?

- tracheids • tracheids are the major component of xylem tissue and responsible for movement of water

MB: Loss of water from the aerial parts of plants is called __________

- transpiration

RG: What functions may a leaf have, in addition to or instead of, photosynthesis?

- transpiration

RG: What are some examples of modified stems? How does each allow the plant to thrive in its environment?

- variation and size allows plants to harvest light at different locations to minimize competition and thrive in wide arrays of habitats

Water Potential Gradient

- water evaporates into air spaces from mesophyll, creating tension - film of water on cell surface decreases • allows for more water to move out of the mesophyll into the edge of the leaf - tension on the H2O inside the mesophyll cells increases - pull on H2O in the xylem vessels increases - water moves up from the root into the xylem and up the plant

Transpiration Wrap Up

- water is acted on by two forces → solute potential and pressure potential - water potential is the sum of these 2 forces - water passively moves to areas of lower potential - the water potential gradient decreases from roots through the shoots to the atmosphere - water moves up the plant by moving down the potential gradient

Why do hydrogen bonds form between H2O molecules?

- water molecules are polar molecules with partial charges due to electronegativity • oxygen → 𝛿- • hydrogen → 𝛿+ - hydrogen bonds form between two molecules that have these partial charges • can form between other molecules, not just water • commonly found between amino acids (side chains in a protein)

Solute Potential (Ψs)

- water moves to areas of higher solute concentration • [ ] = concentration - solute potentials are always *negative* because they are measured relative to the solute potential of water - solutions with high [solute] have low solute potential - water moves towards areas of lower solute potential • remember isotonic, hypotonic, and hypertonic

MB: What would happen if this cell were moved from pure water to a seawater solution?

- water would move out of the cell • the solute potential would be lower outside of the cell, water would move in that direction • remember isotonic, hypertonic, and hypotonic solutions

Q2: Match the part of the plant listed with the tissue system it belongs to

- waxy cuticle covering leaves → dermal tissue - parenchyma cells that undergo photosynthesis and store nutrients → ground tissue - xylem and phloem → vascular tissue

RG: How are plants able to continue growing through their lives? What role do meristems play in growth?

- when meristematic cells divide some of the daughter cells remain in the meristem allowing it to persist - *meristems*: a group of undifferentiated cells, including stem cells that divide and develop into various adult tissues throughout the life of a plant

Appearance of Land Plants

- ~500 mya: colonization of land • first true land plants ↳ "true" → capable of living outside of the water • associated with many adaptations - set up for new radiations on land • plants become less dependent on being near a lot of water • plants on land allowed the capability of animals to evolve and also live on the land (eat the plants for food)