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Diversity - Angiosperms


Can you describe the range of angiosperm diversity (with some examples) in the terms of: growth form and size, habitat, autotrophic/heterotrophic?

  • small aquatic Lemna (duckweed)
  • large terrestrial Platanus (sycamore)
  • desert cactus
  • arctic saxifrages
  • mostly autotrophic (photosynthetic) but some heterotrophic: parasites Cuscuta (dodder) and Arceubothium (dwarf mistletoe) and saprophytes Monotropa (Indian pipes)

If you could not look at a seedling how would you tell a monocot from a dicot?

  • monocots often have parallel veined leaves and flower parts in threes, scattered vascular bundles, never truly woody
  • dicots net-veined leaves and flower parts often in fours or fives, vascular bundles in ring or cylinder and can be woody

What is the critical difference between angiosperms and gymnosperms?

  • in angiosperms seed is enclosed in sporophylls which form one or more carpels of the ovary
  • in gymnosperms seed is on the surface of the sporophyll

What structure represents the sporophyte and are these plants homosporous or heterosporous?

The plant is the sporophyte generation and it is heterosporous.

What structure represents the microsporangia and how does the microgametophyte develop?

Anthers are microsporangia and male gametophyte forms first two cells, tube and generative which divides to form two sperm nuclei.

What structure represents the megasporangia and how does the megagametophyte develop?

The ovule is the megasporangium (not the ovary) and one mother cell undergoes meiosis to form 4 megaspores of which one divides to form typically 8 nuclei (the megagametophyte).

What is missing from the (angiosperm) megagametophyte which was present in the pine?

archegonia

What do we mean by double fertilization and what happens to the gametophytic cells that are not involved in this?

  • Typically three nuclei are at each end of the egg sac, three distal to the micropyle (antipodals) which degenerate.
  • Three close to the micropyle of which two are helpers (synergids) and one becomes the egg which fuses with a sperm nucleus to form the zygote and then the embryo.
  • The other two nuclei in the middle fuse with the other sperm to make the first cell of the triploid endosperm.
  • After this double fertilization, the synergids degenerate.

What is the ploidy level and origin (sporophytic / gametophytic) of the tissues in an angiosperm seed?

  • seed coat and nucellus (if present) diploid and sporophytic (parental)
  • embryo diploid sporophytic (progeny)
  • endosperm triploid (neither sporophyte or gametophyte)

What are the food storage tissues in these seeds?

endosperm and cotyledon(s)

What additional tissues are present in fruits?

  • usually the carpel wall (pericarp, parental tissue) can be dry or fleshy and swollen
  • sometimes receptacle and remains of other floral parts

In what three ways is outcrossing encouraged or ensured in various angiosperms?

  • separate pistillate and staminate flowers on same plant (monoecious) or different plants (dioecious)
  • in dichogamy anthers mature before stigma (protandrous) or stigma before anthers (protogynous)
  • in other plants flowers are perfect but incompatibility genes cause rejection of pollen from the same flower

Does outcrossing apply to all angiosperms?

about half of the species are self fertile and this has often been selected for in cultivated plants

What stage in the life cycle does a flowering plant represent:

  1. gametophyte
  2. sporophyte
  3. strobilus

  1. No this would be true only for mosses, liverworts and related plants

     

  2. Yes, as in most of the plant kingdom the sporophyte is the dominant phase (although alternation of generations still occurs)

     

  3. A flower can be regarded as a kind of strobilus, but there is more to the plant than this

Are flowering plants:

  1. homosporous
  2. heterosporous
  3. non spore forming

  1. Pollen is the most obvious kind of spore produced by flowering plants, but they produce megaspores too,

     

  2. Yes, just like the other seed-forming plants two kinds of spore are involved in the life cycle: megaspores (in the ovule) and microspores (pollen)

     

  3. Flowering plants do form spores, although we do not generally call them that.

Does the male gametophyte develop

  1. free swimming sperm
  2. many cells
  3. three cells

  1. The male gametophyte development is very limited. No antheridia or free living sperm are produced.

     

  2. The gametophyte is formed by only two mitotic divisions

     

  3. That's as far as it goes! The mature male gametophyte contains a vegetative or tube cell and two sperm cells.

The eight cells typically formed in the ovule represent:

  1. megaspores
  2. an archegonium
  3. female gametophyte

  1. Only four megaspores are formed and only one of these persists.

     

  2. Archegonia are not formed in the flowering plants.

     

  3. Yes, typically the female gametophyte consists of one egg cell, two synergids (helpers) a binucleate central cell and three antipodals, making eight in all.

The sperm nuclei travel down the pollen tube to fuse with:

  1. the egg
  2. the egg and the synergids
  3. the egg and the central cell

  1. One of them certainly fuses with the egg, but what about the other?

     

  2. The synergids may help in zygote formation but they do not fuse with sperm nuclei

     

  3. Yes, one fuses with the egg to form a zygote and then an embryo (for the next sporophyte). One fuses with the central cell which goes on to form the endosperm, an important food storage tissue in many seeds.

The ploidy level of the endosperm is:

  1. 3n
  2. 2n
  3. 1n

  1. Yes, one sperm (haploid) fusing with the central cell containing two haploid nuclei makes the endosperm triploid.

     

  2. You might expect this since most tissues are diploid, but it is not.

     

  3. There is no haploid tissue in an angiosperm seed.

A plant with a net-like pattern of veins on its leaves is likely to be:

  1. a monocot
  2. a dicot

  1. It could be, but monocots are more likely to have parellel veins (which dicots never have)

     

  2. Although a monocot may have broad leaves with branching veins this pattern is more typical of dicots.

A plant whose flowers have many petals, stamens or pistils is likely to be a:

  1. monocot
  2. dicot

  1. Monocots never have an indefinite number of flower parts.

     

  2. Yes, dicots in such families as Magnoliaceae, Ranunculaceae and Rosaceae can have an indefinite number of flower parts.

A plant whose flowers have three petals, stamens or pistils is likely to be a:

  1. monocot
  2. dicot

  1. Yes, flower parts in threes is a typical monocot feature (although some dicots can have three or six petals)

     

  2. Dicots typically have 4, 5, 10 or many flower parts (although they can sometimes have three or a multiple of three, so this is not an absolute rule)

A flowering tree is likely to be a:

  1. monocot
  2. dicot

  1. If you are outdoors in Ohio there will be no confusion. Even in the tropics palm trees are not woody in the same way that brodleaved trees are. They have no secondary growth.

     

  2. Only dicots can form true wood and become trees. Palm trees are monocots but they do not form true wood, so they are not really trees!

If you examine pollen with a microscope and each grain has only one pore or furrow it belongs to a:

  1. monocot
  2. dicot

  1. Yes, this is one of the most reliable distinguishing features (although not easily seen!)

     

  2. No, dicot pollen has three pores or furrows. >/ol>

The gynoecium is a collective term for the:

  1. stamens
  2. pistils

  1. No, that would be the androecium

     

  2. Yes, word has the same derivation as gynecology.

A flower in which the sepals, petals and stamens (androecium) are attached below the ovary (gynoecium) is:

  1. hypogynous
  2. perigynous
  3. epigynous

  1. Yes hypogynous means "attached below the gynoecium or ovary".

     

  2. In perigynous flowers the other parts are attached to a sort of cup that half-encloses the ovary.

     

  3. In epigynous flowers the other parts are attached to the top of the ovary (with the style coming through the middle)

A flower that lacks one of the four sets of structures (calyx, corolla, androecium, gynoecium) is:

  1. imperfect
  2. incomplete

  1. Not necessarily; as long as it has at least one stamen (androecium) and one pistil (gynoecium) it is referred to as "perfect"
  2. Yes if any of the structures is absent it is termed "incomplete"

So a perfect flower must have:

  1. sepals
  2. petals
  3. stamen(s) and pistil(s)

  1. No as long as the flower has androecium and gynoecium it can be called "perfect" even if it is lacking other parts.

     

  2. No as long as the flower has androecium and gynoecium it can be called "perfect" even if it is lacking other parts.

     

  3. Yes a flower must have at least one stamen and one pistil to be called "perfect"

If unisexual male and female flowers both occur on the same plant the species is called

  1. monoecious
  2. dioecious

  1. Yes unisexual flowers on the same plant means that the plant is monoecious.

     

  2. No in this case the male and female flowers would occur on separate plants.

If anthers shed their pollen before the stigma is receptive in the same flower it is:

  1. protogynous
  2. protandrous

  1. No this means that the stigma is receptive before the pollen is shed

     

  2. Yes this is one type of dichogamy separating the sexes in time rather than in space.

Primitive flower types:

  1. are incomplete
  2. are bilaterally rather than radially symmetrical
  3. have many petals, stamens or pistils

  1. No loss of one or more flower parts is generally regarded as an advanced feature

     

  2. No radial symmetry is a more primitive feature than bilateral

     

  3. Yes flowers like Magnolia with many petals stamens and pistils are regarded as the most primitive.

Advanced flower types have:

  1. superior ovaries
  2. separate petals
  3. inferior ovaries

  1. A hypogynous flower has retained the primitive arrangement of sporophylls in a simple sequence: sepals, petals, stamens, pistils

     

  2. In more advanced flowers petals, and sometimes other parts have fused to form a single structure

     

  3. Yes in more advanced flowers calyx, corolla and stamens have "migrated" to a point of attachment above the ovary (epigynous)

A dry single seeded fruit in which the pericarp has grown out to form a wing is a:

  1. achene
  2. nut
  3. samara

  1. An achene is a small nut-like fruit (such as a strawberry "seed")

     

  2. Do nuts have wings?

     

  3. Right, samaras are flying fruits, like ash. Maple keys form double samaras.

A dry fruit in which the pericarp splits in two to reveal an inner partition with seeds on either side is a:

  1. schizocarp
  2. legume
  3. silique

  1. A schizocarp breaks up so that pieces of the ovary, each containing a single seed, come away.

     

  2. A legume breaks in two but there is only one row of seeds and no inner partition (as in peas and beans)

     

  3. Right, siliques have a papery partition with seeds on either side. Strictly a silique is an elongated fruit (as in Brassica) and there is a similar rounded fruit called a silicle (as in Lunaria the "money plant")

A dry fruit in which the pericarp splits down one side so that seeds spill out is a:

  1. follicle
  2. capsule
  3. lomentum

  1. Right, a follicle splits open down one side (example: milkweed)

     

  2. Capsules break open with more than one slit (as in tulip) or pore (as in poppy) to release their seeds

     

  3. A lomentum is a special kind of legume with breaks up into sections containing a single seed instead of splitting open. So it is between a schizocarp and a legume.

A fruit in which the ovary wall is succulent and fleshy on the outside but has a hard and stony region enclosing a seed on the inside is a:

  1. drupe
  2. berry
  3. pome

  1. Right, a drupe has fleshy outer pericarp (exocarp) and then a stony endocarp. Examples are cherry and peach, almond and walnut.

     

  2. In a berry the entire ovary wall (pericarp) becomes fleshy and there is no hard endocarp around the seeds. (Examples: grape and tomato)

     

  3. In a pome the receptacle grows up around the seeds to make the fleshy edible part. (Examples are apple and pear)

A fruit made up of several ovaries from a single flower is a

  1. multiple fruit
  2. aggregate fruit

  1. A multiple fruit is formed from the ovaries of several flowers. (example: pineapple)

     

  2. Right, an aggregate fruit can be many achenes (strawberry) or drupes (raspberry) on a common receptacle

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