A] INTRODUCTION

• Plants have adapted to their physical (abiotic or non-living) environment and their biotic (living) environment

• If all the seeds produced by a plant just fell directly to the ground under the parent plant, serious overcrowding of seedlings -  the death of many or most would result.
• Plants have many ways to disperse their seeds
• wind dispersal
• seeds may be dustlike, weighing almost nothing
• seeds may possess plumes that help make them buoyant
• seeds may possess “wings” that increase the seed’s surface area and the likelihood that the seed can be blown away by the wind
• water dispersal
• seeds may contian abundant air-filled spaces that increase their buoyancy
• seeds may have a thick seed coat that keeps them from getting waterlogged
• animal dispersal
• seeds may have spines or hooks that help them adhere to fur or feathers

• Fruits of the juicy kind (e.g. apples, tomatoes, cherries, etc.) are green and bad tasting before they ripen
• Such fruits are not produced for the use of people
• Plants develop fruits as a means of assuring dispersal of the seeds by animals
• seeds from ingested fruits may be spat out
• seeds from ingested fruits may pass through the digestive tract and voided with the feces
• Facts about fruits:
• when fruits are green, the seeds have not yet reached maturity
• when fruits have ripened, the seeds have matured and are ready to be dispersed
• as fruits ripen, many kinds change color from green (leaf-like color) to a different color (red, yellow, orange, etc.)
• as fruits ripen, many change from bad-tasting to sweet and good-tasting
• as fruits ripen, many become easier to pick (i.e. to separate from the parent plant)

• Environmental factors that influence desert organisms - extreme dryness, heat, high levels of sunlight, & wind
• these speed up water loss from the bodies of organisms
• Adaptations of desert plants
• they have a coating of wax (a cuticle) that seals in water
• some drop their leaves during the driest season, thus reducing their leaf surface area and their area for evaporation
• some (annuals) survive the driest seasons as seeds
• some are thick and fleshy
• Thick and fleshy plants are called succulents
• examples include cacti
• cacti are native only in the New World
• in other parts of the world their are desert plants that look like cacti, but are not cacti
• surface area / volume ratios of a cactus pad vs. ordinary leaf (lower for succulents)
• plants lose water through their surface

• Many desert plants are armed with an array of spines, thorns, & prickles - armature
• plants of deserts & other dry regions possess more armature than plants anywhere else
• Facts about desert plants
• many desert animals are herbivorous
• the amount of biomass produced by desert plants is vastly less than that produced by plants in other kinds of areas
• dividing the biomass by the number of animals that are seeking it for food will reveal that there is tremendous “grazing” pressure on available biomass
• Armature is a good defense only against large herbivores, it is not a good defense against small herbivores, such as insects

• Broad-leaved trees are those whose leaves are flat and thin
• Facts about photosynthesis & broad-leaved plants:
• leaves are the major photosynthetic organs of most plants
• photosynthesis in broad leaves does not take place when the temperature falls below about 40o F.
• when the soil is frozen or very cold, the absorption of water by the plant’s root is slowed down or even halted (water is required for photosynthesis)
• broad leaves are injured when the temperature falls below freezing
• broad leaves can lose a lot of water to the environment
• Another major reason to lose leaves - stop damage due to weight of snow on branches

• Plants take up carbon dioxide and give off oxygen
• Water, as a gas, can also be exchanged (taken up or given off)
• For most land plants
• water is lost and must constantly be replenished by water from the soil.
• if plants lose too much water they will wither and die
• plants must balance the capture of carbon dioxide with the loss of water
• Two structures are involved with gas exchange - stomates and cuticle
• Stomates - small holes on the leaf surface through which gases can pass.
• the size of the opening can be changed by shrinking or swelling the cells that surround the opening (guard cells)
• the remainder of the leaf surface is covered with a waxy cuticle
• the cuticle stops the movement of all gases
• the cuticle forces gas exchange to take place through the stomates
• Be able to recognize open vs closed stomates
• There are more stomates on underside than on top of leaf

• Vines - plants that are unable to hold themselves up but must rely on something else for support
• Vines may be woody plants (e.g. grapes) or herbaceous (non-woody) (e.g. peas)
• Three methods that vines use to hold onto and ascent whatever support they use
• aerial roots - roots that grow from stems that are above ground
• tendrils - wire-like structures that function in the support of vines by wrapping around other structures
• twining stems - the whole stem wraps around a support

• Carrots (and other roots like them) are produced by plants that are either annual (living for one year only) or biennial (living for two years).
• Facts about carrot-like plants
• during the first part of the year, the plant produces leaves that grow directly from the top of the root
• there is no above ground stem
• the root becomes crammed with food materials produced from photosynthesis
• during the latter part of the year, or during the second year (biennials), the plant sends up a stem
• the stem produces flowers, followed by fruits with their contained seeds
• the root becomes shrunken and, often, partly decayed
• following the reproductive period, the plant dies
• The roots of such plants as carrots serve as energy storage sites which are later used for flower and seed production (reproduction)

• Allelochemic - a chemical produced by a plant to inhibit or repel other plants and animals
• Allelochemics repel specific competitors
• the chemical may produce a detrimental effect on one herbivore and have no effect on another species.
• some plants produce chemicals that inhibit the growth of other plants
• This is the major defense that plants use against small herbivores, like insects

• Cuticle - a waxy coating on the surface of leaves
• helps to prevent the loss of water from the body of the plant

• The skin of the potato (or of roots in general) serves as a one-way barrier to water
• water can come into the plant from the soil but cannot move out to the soil when the soil is drier than the root

• Winter buds
• each is covered with overlapping scales
• inside the buds are the delicate tissues that will develop into new leaves and stems
• these internal tissues are easily damaged by drying out
• The scales on winter buds protect these delicate tissues from freeze-drying (do not really protect against freezing)

• Some plants use small animals (e.g. insects) as supplements to the nutrients taken from the soil
• In order to capture & digest the animals, each type of plant has evolved a particular modification of its leaves
• These plants live in nitrogen depleted soils and gain their nitrogen by digesting insects (eat to fertilize themselves)
• Venus flytraps do not have muscles to close their leaves, rather they use water pressure and changes in cell size to close their traps