Sexual selection
Selection based on variation in secondary sex characteristics, leading to the enhancement of
sexual dimorphism.
Shark
A person regarded as ruthless, greedy, or dishonest.
Shoot system
The aerial portion of a plant body, consisting of stems, leaves, and flowers.
Short-day plant
A plant that flowers, usually in late summer, fall, or winter, only when the light period is
shorter than a critical length.
Sieve tube member
A chain of living cells that form sieve tubes in phloem.
Sign stimulus
An external sensory stimulus that triggers a fixed action pattern.
Signal peptide
A stretch of amino acids on polypeptides that targets proteins to specific destinations in
eukaryotic cells.
Signal-transduction pathway
A mechanism linking a mechanical or chemical stimulus to a cellular response.
Simple squamous epithelium
Epithelium made up of a single layer of flattened scalelike cells.
simple tissues
A simple tissue is composed of only a single kind of cell, while a complex tissue is composed
of two or more different kinds of cells. In this week's lab, you will be introduced to the
principal simple tissues of the plant body
Sink habitat
A habitat where mortality exceeds reproduction.
Sinoatrial node
Area of the vertebrate heart that initiates the heartbeat; located where the superior vena
cava enters the right atrium; the pacemaker.
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