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By: HWC, Views: 5735

Gastrulation Most animals enter a phase early in development called gastrulation. In this phase, a tiny ball or disc of cells rearranges to form three embryonic layers of tissue, called germ layers. The germ layers of the embryo—now called a gastrula—are called the endoderm, mesoderm, and eco...

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What are the Parts of a Plant Cell?

By: HWC, Views: 5702

Every chloroplast in a plant cell is packed with stacks of flattened sacs called thylakoids. The thylakoid membranes contain chlorophyll, as well as most of the other components required for the light reactions of photosynthesis. The chlorophyll-containing structures within the membranes are c...

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Double Stranded DNA Molecule Animation

By: HWC, Views: 4587

Double Stranded DNA Molecule Animation

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Functional zones in a mitochondrion

By: HWC, Views: 4642

A mitochondrion has a double membrane system. The outer membrane faces the cytoplasm. The inner membrane divides the organelles interior into two compartments. The enzymes that carry out the second stage reactions are in the semifluid matrix inside the inner compartment. Embedded in the ...

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Homologous chromosomes during prophase I - Animation

By: HWC, Views: 4538

The chromosomes were duplicated during interphase and the sister chromatids are now in thin threadlike form. Each chromosome becomes zippered to its homologue, so that all four chromatids are closely aligned. The chromosomes are tightly aligned, but we will show them as separate so that y...

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What is Reverse Osmosis?

By: HWC, Views: 4400

Osmosis is when a solvent, such as water, moves from a low-solute concentration solution to a higher-solute concentration solution through a semipermeable. Osmosis is an example of diffusion (a special case of diffusion) in which the molecules are water, and the concentration gradient occurs a...

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Metaphase I Animation

By: HWC, Views: 4662

This is a cell during metaphase I. For each pair of chromosomes, any gamete produced by this cell could contain either the maternal chromosome or the paternal chromosome. How many different combinations of maternal and paternal chromosomes are possible in the gametes produced by a cell with th...

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Sperm Formation

By: HWC, Views: 4612

Spermatogenesis takes place inside the seminiferous tubules. Diploid spermatogonia located near the outer edge of the tubule divide mitotically to form primary spermatocytes. The first meiotic division produces secondary spermatocytes with a haploid number of duplicated chromosomes. T...

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Mendel's pea plant, Pisum sativum experimental

By: HWC, Views: 4526

Mendel chose the garden pea plant, Pisum sativum, for experimental tests of his ideas about inheritance. Under normal circumstances, the garden pea plant is self-fertilizing. This cross-section shows the gamete-forming structures. Sperm-producing pollen grains form in the stamens. Eggs deve...

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