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General Biology 101
Chapter Outlines
Starr & Taggert
10th edition
Chapter 23
Section 23.5
The Rise of Seed Bearing Plants
Arose 360 million years ago in the Carboniferous period.
Most successful group of plants (in terms of numbers and diversity).
Characteristics of Seed Plants:
1) Pollen
-
sperm bearing male gametophyte
two types of spores
Can drift with air currents (in gymnosperms)
Or can be carried by animal pollinators (in angiosperms)
Pollination – the arrival of pollen grains on the female reproductive structures.
Not the same as fertilization, but just precedes this event.
2) Megaspores
- Develop within ovules, which will become seeds at maturity.
3) Water conserving traits
- Thick cuticle (waxy later).
- Recessed stomata (pores for gas exchange)
- Allows plants the possibility of inhabiting drier climates.
* What people call the “Age of Dinosaurs” botanist call the “Age of Cycads” these are
plants that are gymnosperms and often grow in tropical climates.
Section 23.6
Gymnosperms – means “naked seed”
Seeds are not enclosed in a chamber but rather are “perched” on a spore producing
structure (usually, though not always a cone).
I. Conifers
- Cone bearing plants (usually evergreen trees and shrubs).
- Cones are reproductive structures that bear exposed seeds/ovules on the upper
surface of their scales.
In conifers the leaves may be needle like or scale like.
Examples include: Pines, Junipers, Redwoods, Hemlocks
II. Cycads
-
100 species still in existence (more common in the geologic/biological
past)
Have cones but they form a female cone on one plant and a male cone on
the other plant.
Many have leaves that are quite similar to palms.
Most inhabit tropical and subtropical areas.
III. Ginkos
-
Only one surviving species – the maidenhair tree. Ginko biloba
Once prolific group in the time of the dinosaurs.
Deciduous
Male trees are planted as ornamentals, and they are considered quite
resistant to air pollution and insect damage.
Female trees bear seeds that have a potent stench and usually not
introduced by people.
IV. Gnetophytes
- Trees and leafy vines living in the humid tropics.
- Ephedra shrub is in this group.
- Welwitschia mirabilis is an odd, exotic plant that grows in the hot deserts
of southern and western Africa.
Section 23.7
A Closer look at the Conifers
Pine Life Cycle
Strobili are cones that bear spores (male or female) in conifers.
Megaspores – female  Ovules are on cones.
Microspores – male  pollen grains
For pines fertilization of the egg in the female gametophyte (in the female cone) occurs
one year after pollination by the male gametophyte i.e. the pollen grains.
When one egg is fertilized it will become diploid, a sporophyte and an embryonic plant
that is (protected within the seed coat) and given some nutrients in the seed prior to
dispersal.
Figure 23.17 outlines the steps of the pine life cycle in detail with associated graphics.
See Sec 50.4 on deforestation for further info about issues related to conifer use by
humans.
Section 23.8
Angiosperms – flowering, seed bearing plants.
260,000 species in this group.
The word “Angeion” means “vessel.”
Flowers are the receptacle that contains the female reproductive parts at the center of the
flower
Pollinators – animals such as insects, bats and birds that withdraw nectar or pollen from a
flower and transfer pollen to another flower thereby assisting in the flower’s reproductive
cycle.
Major groups of flowering plants:
I.
II.
III.
Magnoliids – magnolias, avocados, nutmeg and others.
Monocots – Orchids, palms, lilies and grasses. (Parallel veined leaves)
Eudicots – Most are flowering herbaceous plants and most most flowering
shrubs and trees are in this grouping. (Branching leaves)
Endosperm is the nutritious tissue surrounding the embryonic sporophyte in seeds of
flowering plants. Fruits are mature ovaries derived from flowers. Their purpose is to
help disperse embryonic plants inside the seeds to new destinations (away from the
parent plant).
Fruits are mature ovaries derived from flowers. Their purpose is to help disperse
embryonic plants inside the seeds.
Double fertilization is a distinctive feature of flowering plant life cycles. The male
gametophyte provides 2 sperm to the ovule in the flower.
 One sperm fertilizes the egg  embryonic sporophyte.
 The other sperm fertilizes a cell that will become the nutritive endosperm.
Section 23.9
Seed Plants and People
Homo erectus (an early human predecessor) that lived 500,000 years ago in China
gathered food items like nuts, seeds and stored them.
11,000 years ago humans began domesticating wheat, barley and other plants.
3000 species of food plants exist but only about 200 became the major crops.
We also use plants for:
- lumber/building
- textiles i.e. cloth and rope
- perfumes
- insecticides
- flowers for customs and rituals
- medicine
- personal use that could be damaging e.g. tobacco
Section 23.10 is a review section
It includes a summarizing table 23.1 comparing habitats and species numbers of various
plants.