Plant and Animal Development - Exercise 10 Objectives Identify Starfish Development using the models and microscope slides. Understand when sperm penetrates the egg, it creates a membrane barrier. -Understand purpose of umbilical cord and placenta in mammals. -Know primary germ layers.

Pages 1 - 4 is skipped unless your instructor wants you to know this stuff, you have to do this on your own. You will learn more about this in BI108, if you take the class.

All multicultural, sexually reproducing animals utilize gametes to transmit genetic information to their offspring. The contribution to the offspring is limited to their nuclear contends - I.e., a haploid set of chromosomes. Egg cells are typically much larger than sperm cells. They, too, contribute a haploid set of chromosomes to the offspring; however, they may also provide nutrients (for energy and growth), in the form of yolk, to sustain the development of the offspring to the point that it can obtain its own food. There are several different types of eggs with respect to the amount and distribution of yolk.

Those organisms that live independently will usually pass through one or more immature larval stages before reaching their final mature form. The more yolk that an egg possess, the more time the embryo has to develop tissues and organs that will enable it to live indecently. Organisms that develop on land must be protected from desiccation (drying out) by remaining in mother’s body or have a protective barrier. Also, there must be enough yolk to support a considerable amount of development, as occurs in bird and reptile eggs, for example.

The fusion of the haploid sperm nucleus with the haploid egg nucleus at fertilization produces a diploid zygote, which is the beginning of new organism. The first stage of development is cleavage, during which the cells rapidly dividing by mitotic cell division without increase their mass. Each of the cells is called a blastomere. The embryo, therefore, increases its cell number, but it does not grow in overall size. As cleavage progresses, the blastomeres tend to become peripherally located, leaving a space or cavity (the blastocoel) in the center of the embryo. Cleavage ends with the formation of a hollow ball of cells called a blastula.

The next process is called morphogenesis The next process is called morphogenesis. During this, the shape and body form of the organism will be produced and the embryo will begin to grow an enlarge. Some cells will migrate to other locations in the embryo. This movement of embryonic cells is referred to as morphogenesis movements. The movements coupled with the continued multiplication of cells will produce three layers of cells. The three specialized cell layers are called the primary germ layers.

Ectoderm: Outermost layer Ectoderm: Outermost layer. It gives rise to the skin and associated structure and the nervous system. Mesoderm: Middle layer. It gives ruse to muscle, bone, tendons, blood, and other connective tissues. The kidney, gonads and the heart. Endoderm: Inner layer. It gives rise to the lining of the organs of the digestive system, the lining of the lungs, liver, cell of the pancreas and produce digestive enzymes.

Morphogenesis is initiated by the inward migration of a group of cells towards the interior of the embryo into the blastocoel. The particular morphogenesis movement is referred to as an invagination, and during this time the embryo is called a gastrula. The invagination (aka gastrulation) creates an opening to the outside of the embryo which is called the blastopore. As gastrulation progresses, the inward moving cells from an internal cavity called the archenteron, which is continuous with the blastopore. Once the primary germ layers have formed, differentiation of these cells into mature tissues begin to occur.

Starfish Development Models

Early cleavage stage embryos (2,4, and 8 cell stages)

Cleavage

Gastrula

Development in placental mammals Nearly unique to most mammals in the animal kingdom is the protection and nourishment of the embryo (fetus) within the uterus of the mother by assistance of a complex organ called the placenta. There is no active, feeding larval stage in mammals, because the mother and the placenta provide food for embryonic growth through the umbilical cord. Embryos are attached to the umbilical cord with the placenta.

Various mammals in their placenta. -What’s the thing cord that attaches the placenta to the animal for nutrients?

The Umbilical cord…

Chicken Embryonic Stages

Sperm Identify: Sperm head & flagellum

Starfish embryos, various stages Fig 110a - Rust Early Starfish Development Females and males shed their gametes into water where fertilization occurs. These slides contain a mixture of all of the various embryonic stages in whole mounts.

Single Egg cell – Unfertilized egg Before sperm penetration of the egg occurs, the nucleus and a single nucleolus are clearly visible in the unfertilized egg cell. Label: nucleus, nucleolus, nuclear membrane, cytoplasm

Zygote Label: Fertilization membrane Fertilized egg: Once the sperm penetrate the egg, the egg cell (which was actually a secondary oocyte) completes meiosis. The nucleus will no longer be visible. A fertilization membrane is formed, which prevents any other sperm cells from entering the egg. Label: Fertilization membrane

Two Cell Stage Fig. 110C - RUST When a sperm has gotten into the egg, the egg will create a membrane barrier to prevent other sperm from entering. Two Cell Stage Fig. 110C - RUST

Early cleavage stage embryo (2,4, and 8 cell stages)

Early Blastula Figure 110g - RUST

Late Blastula Figure 110h - RUST

Cleavage Figures 110i – 110k - RUST Label: Blastopore & Blastocoel

Gastrula Figure 110l - RUST Late gastrula Label: Blastocoel, archenteron, blastopore, ectoderm, endoderm, & mesoderm..

Larva of Starfish Figure 110m - RUST Label mouth, esophagus, stomach, intestine, and anus

Chick

Page 10 – Lab Book - Questions 1. What stage of development is characterized by an increase in the number of cells but no overall increase in the mass of the embryo? 2. Which of the starfish stages that you drew marks the beginning of morphogenesis?

Page 10 – Lab Book - Questions 1. What stage of development is characterized by an increase in the number of cells but no overall increase in the mass of the embryo? Cleavage 2. Which of the starfish stages that you drew marks the beginning of morphogenesis? Gastrula

Page 11 – Lab Book - Questions Yolk in animal eggs is used for food energy for growth of the embryo until the embryo hatches or becomes a large larva. The starfish egg has almost no yolk and develops into a larva with a complete digestive tract fort eight hours after fertilization. A frog egg has a moderate amount of yolk and develops into a larva (tadpole) 10 days after fertilization. A bird egg has a very large amount of yolk and doesn’t hatch for three weeks. Does there seen to be any connection between the amount of yolk present in a starfish egg and the rate at which the larval stage and its digestive system develops in the starfish embryo? Explain.

Page 11 – Lab Book - Questions Yolk in animal eggs is used for food energy for growth of the embryo until the embryo hatches or becomes a large larva. The starfish egg has almost no yolk and develops into a larva with a complete digestive tract fort eight hours after fertilization. A frog egg has a moderate amount of yolk and develops into a larva (tadpole) 10 days after fertilization. A bird egg has a very large amount of yolk and doesn’t hatch for three weeks. Does there seen to be any connection between the amount of yolk present in a starfish egg and the rate at which the larval stage and its digestive system develops in the starfish embryo? Explain. The more yolk, the longer it takes to develop into a larva and your digestive system isn’t fully developed.

Page 12 – Lab Book - Questions 7. Name several functions of the placenta. 9. Compare how the sperm is transported to the egg in a flowering plant and how the sperm travels to the egg of a starfish.

Page 12 – Lab Book - Questions 7. Name several functions of the placenta. Provides protection, nutrients (food & oxygen). It helps to remove carbon dioxide and wastes from fetus. 9. Compare how the sperm is transported to the egg in a flowering plant and how the sperm travels to the egg of a starfish. In starfish the sperm is just thrown to the water and it swims towards the egg to fertilize it.