Comprehensive Notes on Plant Biology: Stomata, Vascular Systems, Seeds, Gymnosperms, and Angiosperms

Stoma (Opening)

• Plants release $CO_2$ from respiration and require mouths for gas exchange.
• Plants don't have mouths like animals, instead, they have stomata.
• Stoma: An opening.
• Stomata: Multiple openings.
• Plants have microscopic stomata, mostly on the underside of leaves, to allow $CO_2$ and oxygen exchange.
• Stomata open when the sun rises and close when the sun sets, under the plant's control.
• Relative humidity: The amount of water vapor in the air.
• Example: In Miami, the relative humidity is 82%.
• Plants are typically 90% water inside.
• Plants lose water to the air when stomata are open because the water concentration is higher inside the plant than outside.
• If it's raining, the relative humidity is 100%, and plants don't lose water when stomata are open.

Vascular System

• Land plants may or may not have vascular tissue.
• Smaller land plants lack vascular tissue.
• Plants with vascular tissue can grow taller because they can transport water from the ground to the top, reaching heights of 400 feet.
• All land plants have adaptations, but not all have vascular tissues.

Plant Growth at Tips

• Plants grow at their tips, both above and below ground.
• Roots have meristems (stem cells) at their tips that continuously produce more cells.
• Stem cells in plants don't stop dividing and can keep doing so for thousands of years.
• Animals have shorter lifespans than plants.
• Example lifespan:
  • Turtles: Can live a long time; one of Darwin's turtles recently died.
  • Great Greenland sharks: Can live 600-800 years.
  • Bald cypress trees in Florida: Almost 3,000 years old.
  • Bristlecone pine trees in California: Around 5,000 years old.
• Stem cells in plants can function for thousands of years.
• If the tip of a plant is cut off, stem cells at leaf attachment points become active and start growing.
• This is why cutting grass stimulates growth.

Land Plant Collection

• Some land plants have vascular tissue, while others do not.
• Some land plants produce seeds (gymnosperms and angiosperms), while others (ferns) do not.
• Angiosperms produce flowers and fruits, while gymnosperms do not.

Seeds

• Examples of seeds: Mango and avocado seeds, which can vary in size.
• Seeds originated deep in time and offered plants great advantages.
• A seed has three parts:
  • A tough outer seed coat.
  • A food supply (usually starch, sometimes oils) provided by the mother plant.
  • A plant embryo (the next generation), is diploid.
• Beans and peanuts are examples of edible seeds containing a baby plant.
• The most valuable and nutritious part of the plant is often the seed.
• The most important part of the plant is the next generation (the baby).

Seed Dispersal

• Plants have different ways to move seeds around over evolutionary time.
• Seed dispersal mechanisms:
  • Seeds sticking to animal fur or clothing, which are then carried to new locations.
  • Animals eating fruits and dispersing the seeds through their feces.
• Plants trick animals into helping them reproduce and move their babies around because plants are immobile.
• The worst place for seeds is near the mother plant due to competition, so plants use animals to move seeds away.
• Some plants drop seeds into the water for dispersal.
• Angiosperms are the most successful land plants with about 400,000 species because they have seeds.
• Gymnosperms have about 1,000 species.
• Key differences in seed plants:
  • Gametophytes (haploid) are highly reduced and dependent on the sporophyte (diploid).
  • Ovules contain egg cells, which become plant embryos after fusion with sperm.
  • Pollen carries the sperm.
• Diploid organisms have an advantage because they have a spare copy of each gene, which can protect against UV damage.
• Plants with seeds have an advantage over earlier plants with spores.
• Advantages of seeds:
  • Protection: The seed coat protects the embryo.
  • Nutrition: Seeds provide the embryo with a food supply to get a good start.
  • Dispersal: Seeds can be dispersed by various means.
• Avocado seeds are large because they contain a lot of nutrients for the embryo.
• Extinct giant animals in Central America used to disperse avocado seeds.
• Humans saved avocado trees from extinction by cultivating them and breeding them to have thicker skin and bigger fruit.
• Modern bananas are sterile and do not have seeds because humans have hybridized them.
• Bananas are propagated using stems that are genetically identical to the parent plant.
• Most plants we eat have been cultivated by humans for at least 10,000 years.
• Tomatoes we buy are octoploid (eight copies of each gene) because humans have bred them to be larger.
• Wheat used for bread has also been cultivated for thousands of years.
• Seed dormancy: Seeds can last a long time if the seed coat is not broken and water cannot enter.
• Plant embryos wait for water to start mitosis.
• Seeds can remain viable for many years.
• Example: Seeds from a palm tree in a pharaoh's tomb germinated after 1,500 years.
• Seed advantages:
  • Protection: Tough seed coat.
  • Developmental stage: Seeds contain multicellular plant embryos.
  • Genetic diversity: Diploid embryos have more genetic variation.
  • Dispersal: Various methods for seed dispersal.

Gymnosperms

• There are about 1,000 species of gymnosperms.
• Gymnosperms have naked seeds that are not enclosed within a structure.
• Most gymnosperms are hermaphrodites, producing male cones with pollen (sperm) and female cones with eggs.
• The female cones contain the seeds.
• Gymnosperms and angiosperms do not have sperm that swim.
• Pollen in gymnosperms and angiosperms grows a tube to deliver the sperm to the egg, which is more efficient and does not require water.
• Gymnosperms include some of the tallest plants, reaching heights of 400 feet, and some of the oldest plants, older than 5,000 years.

Gymnosperm Reproduction

• Gymnosperms do not undergo double fertilization.
• The embryo in a gymnosperm seed is diploid.
• Nutritive tissue in the seed is also diploid.
• Gymnosperms do not make flowers or fruits.
• A fruit is a ripened ovary.

Angiosperms

• Angiosperms are the most successful group of land plants with 400,000 species.
• Seeds are always inside a structure (carpel).
• A fruit is a ripened ovary plus any associated tissue.
• The carpel protects the babies.
• The carpel arose from a leaf that enclosed the seed.
• Flowers have multiple carpels.
• Tomatoes have many seeds because of the multiple carpels.

Flower Parts:

Perfect Flower

• A perfect flower has all possible parts and is a hermaphrodite (both male and female).
• About 70% of all flowering plants are hermaphrodites.
• A perfect flower has four whorls (layers).
  • Outermost whorl: Sepals (protective leaves).
  • Next whorl: Petals (usually brightly colored).
  • Next whorl: Male part (stamen) with anthers that contain pollen (sperm).
  • Innermost whorl: Female part in the center, with the ovary containing the egg.
• The ovary is enclosed within the carpel, providing another layer of protection.

Pollination:

• Pollen is transferred to the stigma (sticky surface on the female part).
• Flowering plants often use animals to transfer pollen.
• Hummingbirds and bees are common pollinators.
• Pollen grains germinate and grow a tube through the tissue to deliver sperm to the egg.
• Angiosperms and gymnosperms do not have sperm that swim; the pollen tube delivers the sperm.

Double Fertilization:

• Inside the ovule within the ovary is the female gametophyte with only seven cells.
• Angiosperms undergo double fertilization: two sperm are delivered to the female gametophyte.
  • One sperm merges with a cell that has two nuclei, forming triploid tissue (3n), which becomes the endosperm (food supply for the embryo).
  • The other sperm merges with the egg cell is haploid cell (1n + 1n = 2n), forming the diploid zygote (2n), which becomes the embryo.
• The triploid endosperm is the food supply for the embryo inside the seed.

Seed Structure:

Structure

• Seed coat
• Triploid endosperm (nutrient supply)
• Diploid plant embryo (zygote)
• Sperm, made inside every pollen grain, can grow to the egg.
• Do not need water to grow.
  *
• Gymnosperms and angiosperms - sperm do not swim.

Plant Diversity

• This section discusses the wide range of plant diversity and structures.

Comparison of Plants

• Overview of key tables summarizing the differences and plant structure.
  Plant Tissues and Organ Systems
  Three Tissue Types
  Plants have a simple structure versus compared to mammals, however, they're very successful.
  Outer layer
• plants have a outer protective layer called a cuticle to seal in water.
• Plants stomata is controllable and can be opened/closed.
• Plants have xylem and pholem vascular systems that deliver water and nutrients to cells.
• xylem and pholem are like veins and arteries contained vascular systems. Blood contains oxygen and nutrients delivered by a pump-close vascular system.
• Xylem pulls water from ground. Pholem delivers water from green parts.